I've been using Vista for a year on a Thinkpad T61 (C2D 2.2) which came with it pre-installed. I also use XP on my corporate T61 (C2D 1.8).

I had been intending to remove Vista and install XP on the personal laptop, but it's "not that bad". That said, it still bugs the heck out of me in certain things (particularly networking, and in particular Wireless management). I experienced a few BSoDs and lockups pre-SP1 but it has been relatively fine since then.

I like XP better though; and I was an early adopter of it and really liked it over NT4 and W2K.

I'm a Unix user by heart (and by profession), my laptops are mostly just web browser/email (although the BB plays the majority role for that these days)/Word/Visio, and dumb clients for SSH and X to the places of real work...