I have been running windows 7 for a while now. It has gone so well that I have converted all but one windows machine over. My windows media center I have kept with Vista so I did not have to change anything.
My everyday development machine is now Win7 x64. It has a pretty small footprint and runs Virtual machines perfect. I have also migrated my Netbook (MSI Wind) to windows 7. that works great. It is a great OS for a netbook.
So far M$ has impressed me with 7. Faster and simple.