Ted Leung is right on the technical issues here, but not on the wider buzz:
Lots of people are up in arms about IM clients. People are complaining about the Windows client for Google Talk. People are complaining about the lack of Mac and Linux clients. But I think that this is misguided. The real value and potential in Google Talk is that Google might be building an open, un-siloed IM network. It will be interesting to see whether "don't be evil" actually works in this case, because starting another closed, siloed IM network would definitely count as evil (not to mention pointless) in my book.
To be specific, the bleeding edge technology-philes are "up in arms". The users don't care. I say this based on one of the main target customers for IM technology - middle school and up age kids. My daughter is an avid IM user, as are most of her friends (the exceptions being kids with parents who don't allow it). The lot of them use AIM. I've never heard them complain about not being able to chat with so and so due to the silo problem - all the kids just download AIM and move along.
Which is why there's no real pressure to fix this - from the standpoint of the vendors, there is no problem - our rantings on the subject just don't matter to them.