Doesn't work at least with Home Premium version. Bootcamp assistant says 2012 iMac only supports 64bit installations. Bummer. Stupid legacy work programs only support 32bit.
Googling brings this up in other threads. I don't understand why it should be a problem though, on my 2011 MacBook Air (Mountain Lion) I'm running Windows 7 Ultimate 32-bit in Bootcamp, plus Windows XP Pro under Parallels.
Not as good as running native bootcamp. You have to share VRAM and I think you're going to take a bit of a hit on fps. This will be an issue with latest games. On older games, probably should be fine but I would probably still use bootcamp for gaming.