A problem both 360 and PS3 have as games consoles is the games. Both MS and $ony have gone for the top graphics and complex plots/gameplay games which take weeks to get into. Thats fine for teenage kids, but then the consoles and games are mostly priced out of that market. Virtually all of these games are not shareable, so a group can't sit and have a laugh.
Nintendo has got it right for adults with the Wii, as can be seem from the success of the console, easily outselling XBOX360, PS2, and PS3 together every month. The console is fairly simple, not particularly powerful, but the games are instantly 'pick up and playable' and are great fun when a few of you get together on the sofa. Most games are playable by a group, and the innovative control system adds to the fun.
If I was to buy a console for games (my 360 is purely and extender for MCE, not games), it would be a Wii, as its simply more fun than that anything MS or Pony and trap can offer.