Yeah, for a long time only Windows Messenger had built-in videoconferencing. Then along came MSN Messenger v5.0, which could now be installed on XP, but it used the same videoconferencing hook...and as a result, neither client could do video over a firewall without jumping thru a lot of hoops.
With Logitech bits, MSN Messenger videoconferencing can now be done over firewalls. In addition, videoconferencing via MSN Messenger is no longer XP-only, you can now do video on downlevel operating systems as well (except Win95). However, starting video is a pain...you invite the other person to receive your stream, then the other person has to invite you to receive their stream. What, no audio? Now you have to invite the other person to start audio. Maybe they'll do something about this sometime...
AIM won't be doing videoconferencing anytime soon, unless AOL opens their system to allow other clients to IM with AIM clients.
Customizing the appearance is one of the coolest things about v6. Back when the leaked build of Messenger v6 first hit the 'net, I created some themes based on The Matrix for it. Ended up almost exceeding my bandwidth allowance from Ripplehost in just three weeks.
Mess.be is hosting visitor-submitted display pics and custom emoticons for others to download...not sure if they'll ever start hosting convo UI backgrounds, tho' (they used to say they will...). The Express Yourself tab takes you to the Messenger Community, where MS hosts visitor-submitted graphics, including convo UI backgrounds...tho' some idiots don't know how to upload, so you'll see custom emoticons in the backgrounds section, display pics in the custom emoticons section, etc. Occassionally you'll see the neked babe (just before it gets deleted).
The games are kinda simplistic, but have become extremely popular. People in other locales are complaining cuz they can't play yet. As I understand it, more games are coming, then they go world-wide, blah-blah-blah.
Personally, I think v6 has the best-looking and easiest-to-use user interface of any of the IM clients.