LCF has a review on the new Google Talk. Check it out

Google Talk is light weight (< 10MB system memory), simple and Mac OS like beautiful interface. To add a friend, you can search your Gmail contact list from Google Talk. Or send an invitation email.

The chat window can be collapse or expand. However, there is no emoticons (thanks, google!). Also, it does not support file transfer (yet?).

Google Talk is actually using Jabber IM protocol. Therefore, other Jabber IM clients may connect to Google Talk server, too! See the Google Talk IM clients compatible list.

Currently, Google Talk only support Windows platform. OSX user can use iChat to chat with other Google Talk users, and Linux user can use GAIM.

Google Talk Announced