Still running XP on my main machines, Ubuntu to have a play with it (seems very nice). Win2000 on some older machines.
Win7 seems fine, will end up running it one day, but I'm not going to rush out and throw $$ at Bill Gates to get it.
We are now selling Win7 machines at work, we avoided inflicting Vista on most of our customers. A few compatibility issues with old software etc. Nothing buying a new server and upgrading the accounting system wont fix.
Ian