I'm using issues on github to track both bugs and feature requests. I have issues for most of your suggestions, and I'll some more for the ones I don't have. You can also comment on the issues directly.
User profiles for each identity. Just a text field users can fill with information like the Bitcoin address, Dwolla ID, mailing address, etc. if they so choose.
I think the user profiles for identities would be a good idea. For bitcoin address and etc, I have the following issues created:
https://github.com/macourtney/Dark-Exchange/issues/23https://github.com/macourtney/Dark-Exchange/issues/24I also have an issue for viewing an identity:
https://github.com/macourtney/Dark-Exchange/issues/11This could be expanded to add a profile.
PGP integration for the messaging features (are messages public?)
First, messages (which can only be sent on trades right now) are not public and are automatically signed (though the signature is stripped off when saved). Actually, all data sent between Dark Exchange nodes are both encrypted and signed.
I don't want to integrate PGP if I can avoid it since that would add yet another program for people to install when installing Dark Exchange. On top of that, encryption and signatures are already supported in Dark Exchange. We just need to figure out all the ways we want to use them.
Do you think sending messages directly from identity to identity should be supported? If so, how do we get around the email issue of unsolicited messages? Make people friend each other first?

web-of-trust style user rankings, but that's already been requested.
Tracking issue:
https://github.com/macourtney/Dark-Exchange/issues/22Minimize to systray + systray notifications for new messages, accepted trades, etc.
Good idea. I just added a new issue for it:
https://github.com/macourtney/Dark-Exchange/issues/25Some kind of remote API (i was thinking about android apps, but i2p's memory requirements are to great, so a front end is all that seems doable)
I'm worried about this since it could open people up to hacking. However, I created an issue for it:
https://github.com/macourtney/Dark-Exchange/issues/26