The fact that Adium so seamlessly integrates accounts is definitely a plus. Messaging Google Talk contacts was totally transparent.
Google Talk has some excellent integration with Gmail, too. Try sending an gmail to another Gmail address: That person is automatically added to your contact list. If you manually add a contact to Google Talk, their alias info is automagically grabbed and implemented, while their email address is added to Gmail.
This is probably all part of Google’s world domination plans (is that not getting a little cliché?), but it’s so darn cool that I don’t care one snitch! No message limit, unbelievable sychronicity, and the fact that it’s Google all make me wonder: Can they take on AIM and, more importantly, MSN?