I'd like to see wallet encryption and multiple wallet support first. The rest is just icing on the cake.
Agreed -- the thing with wallet encryption is that it is still experimental, and not in any official release of the client yet (only in git), so I'll add a big experimental banner.
Anyway, thanks for doing all the work on this, it's really coming together nicely!
Thanks!
edit: splash screen would also be awesome. i know its mostly eyecandy, but the startup right now gives a totally horrible first impression.
And also easy to implement!

When can we expect Bitcoin-Qt to be merged into the main tree, and released as the official client?
I don't know. From what I understand from Gavin on the mailing list, he wants the upcoming releases to be dedicated to bug fixing not major new features. If that's the case, I'll do a parallel release for a while. It just costs some time to build and distribute proper binaries, which I rather spend on development, but hey if there's no other option
