I have seen many different varities, but never a 1L barrel.

F2Pool

Who holds the private keys?

Yes, but have in mind that Trezor provides higher security than what you can get on an android device, and by having the same master seed on two platforms gives you the least common denominator... Security wise.
So, I would only do that if my phone was broken.

The latest generally available version is 1.3.3, and the  release notes were published here:
I have added the above to the OP

(You can see all the releases/tags in the GitHub repository here: https://github.com/mycelium-com/wallet/tags but unfortunately we haven't linked the release notes of the individual versions to the GitHub repository.)

Can you elaborate on that?

Pretty cool stuff 

With Mycelium 2.0 we migrate away from using data.xml and store stuff in a sqlite database instead, so there will be a bit of coding to get it out going forward.

1. No issues. This is perfectly fine.
2. Yes
3. We scan 20 address ahead on the external chain to comply with account lookahead discovery as dictated by BIP44

Correct, you have a choice.
But, the wallet will no longer let you create new random legacy accounts (create a new random key), you can however import a private key that you have made elsewhere by selecting Advanced when creating a new account. In that scenario we expect the user to know what he does and that he has the private key stored safely outside the wallet. It will not be part of the HD account backup.

We really wish our users to be safe and not loose funds because they sent funds to a key that they cannot recover.

You should really try it out. Everything is available for the testnet, where you can play around with worthless testnet coins: https://play.google.com/store/apps/details?id=com.mycelium.testnetwallet
Once you have it installed you can get free testnet coins by "buying" them  (for free) from Virtual Trader when you click Buy / Sell Bitcoins

With the current version of Mycelium you can go to the Keys tab and see the addresses you are working on. Some of those addresses have a key associated with them, they are the ones you can spend from. The ones without a key are so called read-only addresses, you can monitor them but not spend from them.

With Mycelium 2.0 the Keys tab is renamed to Accounts. All your existing keys/addresses are now called accounts and work like before. Those are the ones I call legacy accounts.

In addition you will have one or more Hierarchal Deterministic  (HD) accounts following the BIP32/BIP44 standard. An HD account is one that automatically generates new addresses as you use the wallet for sending and receiving. This means that you get much more anonymous (today anyone who knows your Mycelium bitcoin address can see all transactions associated with it).
Furthermore, because we now have BIP32 support this means that one backup of one secret is enough to generate all the private keys/addresses you will ever need for all the HD accounts you will ever need. Everything can be deterministically generated from one secret. The backup mechanism we use follows the BIP39 standard, and basically involves that you write down 12 random words on paper.

As a user you will not have to worry about all of those addresses, they are managed internally.


Today Mycelium lets you monitor 20 separate bitcoin addresses. For some of those addresses you also have a key (the default), which lets you spend from them

In that case, after the 2.0 upgrade, you should just keep using your existing (legacy accounts) and cold storage spending. They continue work as they do today.
The main benefits of using the new HD accounts are to be more anonymous and only making one backup ever.

Yep. Go to the Keys tab, select a key, then choose Sign Message.

The current version does not use separate change addresses, but the next version will. However, this is unrelated to being able to spend 'change sent back to self'. When you send a transaction you almost always have a change output which goes back to one of your own addresses (unless you spend exactly all value of your unspent outputs). Most wallet implementations allow you to spend that change immediately without confirmation as you are not expected to double spend yourself.

We are thinking about multi-sig, but it will have to wait until we have BIP32/39/43/44 under our belt, which will happen in the next release.

By offline signing I guess you mean the ability to transfer sufficient unsigned data to an offline wallet, have it create a signed transaction, and then transfer the transaction to the online wallet. We have been thinking about that for a long time but there are a few things holding us back.
1. For security reasons it is not enough to just transfer the unsigned transaction offline. You need to transfer all the complete set of transactions that fund the new transaction. This allows the offline signer to verify that you do not pay an exorbitant fee. This can easily mean tens or hundreds of kilo bytes of data. Using animated QR codes will not suffice. You need something like a USB stick or a bluetooth (which may open another attack vector)
2. It requires you to use a second phone for only that purpose, which will be a turn off for many users.

I am not saying that we will not do it, but it is not as trivial as it may seem.

From day one Mycelium has allowed you to send "unconfirmed change sent to self" just like the satoshi client. So you won't have to wait for a confirmation to send the next transaction. You can however not spend coins sent from another address before it has confirmed. This also applies to the HD upgrade.

We don't currently have it on our roadmap.

Mycelium 2.0 for testnet ALPHA 6 released to the play store, and should be available in an hour or two.

A lot has changed since the Alpha 4 release. Some of it:
 - We are now based on BIP39 word lists for backup / restore. You only need one backup forever, and no more encrypted PDF backups
 - When you install Mycelium for the first time you are asked whether you want to create a new wallet or restore a backup (Restore is Trezor + wallet32 compatible (BIP39 + BIP44)). Your first account will be an HD account
 - When you do an upgrade from version 1.x a new master seed and the first HD account is automatically created
 - We nodge users to make a backup by showing a "Secure My Funds" button if no backup has been made yet + if one of the HD accounts have funds.
 - We nodge users to move funds away from 'legacy' accounts by showing a "Secure My Funds" button if a legacy account has funds.

Note: when upgrading from Alpha 3 to Alpha 6 the account names will disappear. Once we hit production the 1.x names will be properly be migrated from your classic keys/addresses to accounts.

If you are a translator you'll get a notification later today for all the new HD strings. Let's get this baby out.

Screenshots would be interesting. Please share here or send them to developers@mycelium.com. Also, what device are you using?

Thanks.
You can do this already, but maybe it is not that obvious. "BTC" is an icon, and if you click it the valuue turns into your selected fiat currency.

You can set the notification email address in settings.

You cannot see old receiving addresses directly. In general reusing address makes you less anonymous. There are two workarounds however:
1. You can select a transaction in an account and 'Show Details'. This will list all the addresses participating in the transaction. If the transaction was you sending, then the input addresses will be yours.
2. You can select an account and select 'Show Unspent Outputs'. This will list those of your addresses that have funda in them.
In general I think we should all be moving away from directly managing/using addresses.

You cannot directly view/export the root public key from the master seed. You can however see the BIP39 word list (in settings for now as a debug thing). We are probably going to add a feature that allows you to properly export the master seed word list. That list can be imported into other BIP39 compatible tools.



 

(If you wish to migrate then I think it is a better idea to send the funds using a transaction.)

The clipboard button automatically gets enabled if you have a private key on it in SIPA format.
Here is an example:
KwWVqndQMw1DyL4Sb2moNArofcQztswhGbSkX2M9mhDBv6BtZ6gW

DON'T use it except for testing purposes!

On some phones there have been problems with the clipboard, so alternatively you can turn it into a QR code using some software you trust.