I used to love MSN messenger when I used Windows (and still do when I use it). The OS X version, though, is a huge disappointment. Microsoft has this thing where they only like to update the program, oh, every year and a half or so. MSN doesn't have any video/audio capabilities like the Windows version, either. Given, Adium doesn't have them either, but Adium is a lot more stable. Adium also has the advantage of a single-window interface for your IMs, separated by tabs rather than separate Windows (a huge space saver). Also, if you do ever get another type of account, or even a second MSN account, the ability to have all your accounts integrated, and use them all at once is a huge plus.