Second Life (via Virtual Ability Island). So I rerolled an avatar (with the somewhat hippyish name of Asha Serenity) and ducked in. I remembered enough from my last half an hour in-world to teleport to the island while my friend, in her best tour guide mode, took me round. Midway through the tutorial, the issue of perspective came up and I had to figure out how much of my avatar's rather shapely butt I wanted to see. I quickly discovered first person is a must for reading signs but the rest of the time, I prefer having the camera positioned a metre or so behind my avatars head. Even in other games, I seldom use first person unless I have to shoot a bow or look at something close up.
However I know quite a lot of people who play MMOs in first person -- many of them seem to be seriously into RP and want to literally 'become' their avatars. So, constant readers, I ask you do you prefer first or third person when you play? Do you change perspective depending on when you raid or how much of the screen you need to see?