From the GMail homepage:
Chat with your friends from right inside Gmail. There’s no need to load a separate program or look up new addresses. It’s just one click to chat with the people you already email, as well as anyone on the Google Talk network. And now you can even save and search for chats in your Gmail account.
We’ve started rolling this out to all Gmail accounts, so yours should have it soon. It’s good to chat.
It will be interesting to see not only how this affects the use of AOL’s AIM, Yahoo Messenger and other IM software, but social networking sites like MySpace and traditional chat sites like Yahoo. If you recall, Yahoo has had problems with minors seeing adult content in chat rooms, and then of course there’s the whole child predator issue.