A company can create "skins" for GoogleTalk that would allow the chat to be in a branded environment. Every 5-10 minutes, the users would see a 10-second advertisement for the brand.
Yahoo! offered this option years ago with its messenger product and it was very popular with advertisers. While this would not be for every demographic set, it might work well with pre-teens and teenagers. Imagine them chatting in an environment with Hanna Montana, Hillary Duff or John Cena.
I think itís critical for Google to take this further by adding in newer technology such as Flash and Ajax. Interactivity with the characters and the brand would make this very sticky.