Don't have it installed, but I'm using it. I'm connected to Google Talk using Gaim.
The Google Talk client itself is still very feature-poor, and it's very spartan (much like Google itself), but I like it that way because it's clean and simple. Google's home page is so refreshingly clean compared to MSN's or Yahoo's. Likewise, I like how Google Talk feels clean whereas MSN's is so busy and noisy and AOL's is ad-ridden and equally unclean.
Having said all that, I'm happier using Gaim for all my IM services, and since Gaim can be used to connect to GT, I don't have Google Talk installed.
I think that the really really cool thing about Google Talk is that it's using an open protocol (Jabber) so that there are already a lot of apps like iChat and Gaim that support GT from the very start. None of the proprietary crap that AOL/MS/Yahoo is using. There will be no attempts by Google to shut off access to its service from other IM clients. In fact, it has been reported by the NYT that Google is encouraging the other instant messaging services to support Google Talk. Remember how MSNM tried to add AIM support and then there was a long period of cat-and-mouse where AOL tried to stop Microsoft from doing so by changing things around over and over? Well, now if MNSM tries to add GT, then not only will GT not try to stop them, but they'll encourage it. I love this "do no evil" philosophy of Google. I think that they're hoping that, in the end, by getting everyone to add support for GT and by embracing an open protocol, their network will come out on top and end up doing what no other company has succeeded in doing: unifying instant messaging. :bigsmile: And if in the process of doing this, they allow this to be a demonstration to the world of the benefits of open standards vs. proprietary stuff, then all the better!