W00t! Google Talk has been released! I just downloaded it this morning and have been playing around with it. The interface is very clean and simple. When you try to type a smiley :-) it highlights it in blue--no "emoticons". There is a setting in the options called "Save recent chat history" that might come in handy, then again, if you're concerned about privacy, you may want to disable this.
According to the Google Talk Wikipedia entry, "Google have announced that a major goal of the Google Talk service is interoperability." This interoperability is made possible by the use of the Jabber instant messaging protocol, allowing users of other Jabber-based IM clients (including iChat for Mac and GAIM for Linux) to connect to Google Talk.
On the Google Talk website it also talks about being able to "talk through your computer but hear your friends as if they were in the same room," referring to the client's built-in VoIP (voice over IP) capabilities. According to Wikipedia, the voice chat function is currently available only for Google Talk users and does not extend to other platforms, but will be extended to other clients in the future.
The Google Talk client is currently only available for download for Windows XP/2000, however, Mac and Linux users can use other clients to connect to Google Talk. This means that my Mac buddies who use iChat can finally IM me without having to use Yahoo! IM or other IM clients. No doubt Google Talk will become more popular as more and more people start using Gmail. In fact, in order to use Google Talk, you need to sign up for a Gmail account. It is still in the beta stage, so expect more features as development continues.