I downloaded and began experimenting with Google Talk last night (reviewed here by sister-site Download Squad here) and I have to say I'm impressed. As with most other Google products it's clean, incredibly intuitive and not nearly as clunky from my persepective as other IM products I'm played around with.

What it's missing right now is any advertising. Don't worry though media buyers, I'm sure that's coming after a suitable beta period. Everything Google has done, with the exception of Google News, has been done with potential advertising in mind. Much like GMail (now publicly available, and which you have to have to get Talk) Google will likely analyze keywords in your previous conversations in order to deliver contextually relevant ads to you doing your IM sessions. The potential even exists to deliver new ads based on your current session, with new matching being done between what you type and AdWords keywords everytime you hit "Enter". I'm sure those who have faired well with their AdWords programs in the past are just waiting to increase exposure via this new feature.