Just as a matter of habit I usually wait six months to a year before moving to a new Windows OS. Gives them time to patch the worst bugs and for third party developers to write updated drivers.
This is a great policy! I recommend it and do it as well, except when I was really itching to get away from some Vista quirks.
When Win 7 Service Pack 1 came out, I waited quite a few months before letting it install. I know several people with use cases similar to my own that had troubles with SP1, but these were ironed out smoothly. I didn't want to be an early adopter.
Marc