Fanfare: Google Talk is now available for the iPhone. It features a snazzy interface (is it possible to create a shoddy interface for the iPhone?) and almost everything you can do on the desktop client: create a quicklist of favorite users, search, and manage multiple conversations at the same time.
There's one problem, though, which makes the entire thing almost useless. The official quote goes like this:
Therefore, you can't have Google Talk sit idly in the back and have a conversation every now and then - which is the default pattern of usage for most users, I believe. This limitation is due to Apple's silly "apps can't run in the background" rule, the official explanation of which goes along the lines of "we can't let people do that, it would consume too much battery." I've warned about the problem before, the most obvious issue is with IM clients such as Google Talk, but I'm sure there are other types of applications that will suffer from it.