As far as multitasking goes, the version of Winblows that can hold a candle to Mac OS X's multitasking doesn't exist. Oh, and networking? Theres another area where Mac OS X (and former Mac OSes to boot) blow Windoze out of the water.
Online gaming? Well, maybe not Evercrack, but Mac users have been playing games online for years - much longer than PC users have (Bolo, anybody?). In any case, online games do still exist for Mac OS, with new ones coming, too (World of Warcraft, for instance, or whatever it's called).
By the way, try putting more than 512MB of ram in a computer running any non-WinNT operating system from M$ . . . heh, heh . . .
The bottom line here is that there isn't anything you can do on a Wintel machine that you can't do on a Macintosh. Often times you won't be using the same apps, but you will be getting the same functionality (minus M$'s bloatware, to boot).