As opposed to what I was expecting until a few years ago, the IM fraternity, instead of unifying into a single, interoperable platform has more-or-less unified into two islands.
ICQ-AIM-Gtalk forms a formidable camp. The MSN-Yahoo! alliance seems similarly impressive. If we discount the innumerable social-networking specific messaging platforms, we are now left with 2 platforms that don't talk to each other. While 2 is definitely better than the fractured platforms we had until recently, I would have much preferred having only one IM client resting on my system tray.
While Google's disposition towards open standards has become an industry benchmark, the others are yet to follow suit. Microsoft carries a legacy thought process that it's not willing to jettison - and with good reason. Yahoo! isn't nimble enough to learn the changing rules of the web and AOL is beset with its own problems.
I've waited long enough to see the unification of IM. Getting so near and yet so far is very frustrating.