I use Win XP at work (no choice, except of course when I've got my MacBook with me, which is nearly every day) - so that'll chance when/if my employer's IT people choose to change it.
As for Boot Camp on my two Macs, on the occasions I need to use it, it has Win XP installed and I suppose it'll stay that way for a while. One piece of software I need it for, a VPN client to get into the hospital's network from off-campus, doesn't work on Win 7 RC (I've tried). The VPN client works on Vista, but then Vista screws up an entirely different piece of software I need. So, the only version of Windows that works with all the software for which I need Boot Camp is Windows XP. So until that changes, it'll have to stay with XP.