This is lovely little app.

Here's some suggestions:

• "From Camera" is an enormous button.  Smaller would be nicer.  In fact, what about a little camera icon next to the receive address text field...
• ... the address on the send page should be a text field; that can be pasted into.  (Say I want to deposit to Mt.Gox, there is no QR code to scan; and even if there were I can't take a photo of the QR code on the phone's screen)
• Copying the account address to the clipboard should be possible. This is so it can be cut and pasted into a website (say I want to withdraw from Mt.Gox to my Instawallet address)
• How about integrating the APIs for Mybitcoin, Mt.Gox and Tradehill accounts as well?  It would be very cool to be able to switch to any of my online wallets and have the same UI for all.
• The balance should be displayed larger and should be outside the tabs (and "account" and the address for that matter).  Balance is neither "send" or "receive" related; and is arguably the key thing we want to know about the account.
• Ability to program our own Instawallet URL.  I already had an Instawallet.  It would have been nice to be able to connect to it instead of having BitPay make a new one.
• Updating balance should be done in a different thread.  During update the UI freezes, changing tabs isn't possible.
• When selecting the "amount" field on the receive tab to enter a number, the keyboard is in alphabetic mode.  We're never going to want to put letters in an amount field; set the keyboard to numeric mode
• The "amount" field on the send and recieve tabs should be in the same physical position on screen
• The screen real estate used by "Account: instawallet.org" is a bit of a waste; can't that be on the credits page?  We don't need to see it all the time.  Perhaps you're planning multiple account support in the future?  In which case I withdraw this point.
• The amount fields should all have more than two decimal places shown when they are showing zeros (or any other number)
• A widget that can be dropped on the home screen to show current balance