My wife and I combined used to have about 6 computers between us of various operating systems, with most of mine dual or tri-OS boot. Now we have simplified and are down to a single computer each, with just Mac OS X running, it is great!
I have a 1.6 / 80 MBA which I use mostly for work. It had Parallels XP initially, then boot camp XP for more speed specifically for World of Warcraft. Once I installed CoolBook to underclock / undervolt, I found I could play World of Warcraft on my Mac so I deleted Windows XP completely and it is 100% Mac OS X now.
My wife has a 1 year old or so MBP 15" and she mostly uses it to play World of Warcraft which runs great on it.
So we've simplified things and are down to just 1 computer each pure Mac OS X family and love it
Also, we each have an iPhone and are planning on upgrading to 3G.