Now you can do more useless things than ever before! Remember tedious crap like winks from 6°? No, you don't? Oh, wait, that's right. That was yet another "wildly innovative" Microsoft product that virtually no one was aware of, much less downloaded, installed or used. Whoops.
Anyhow, there is actually some good stuff in Messenger 7. If anything it's prettier than 6.2 was [although yes, Brian, there is still advertising in the client]. Me, I especially like the "Show what I'm listening to" option - it's integrated with Windows Media Player 10. k3wl d00d!!!
Bonus geekiness: Try doing Actions | Send Other | Send a Message to an MSN Direct Watch. Yes, it works. No, I have no idea how useful it is.