I am already using Windows 7 RC as my primary OS. It's so much faster than XP and the UI improvements are fabulous. Vista was just a beta version of Windows 7, or another Windows ME. XP lasted me almost 10 years and I figure 7 will do the same.
The multiple monitor support has been flawless for me, even with out of the box drivers. Throwing windows around between 3 monitors with "Start+Shift+(left/right)" really speeds up my productivity when programming.
Integrated desktop search is a huge win: fast and accurate. The new taskbar is a big improvement in managing multiple windows, especially when you have 3-4 powershell or cmd windows open. Mouseover the taskbar icon, and you see previews of all your open windows.
The UI is also very responsive and snappy. Bootup times are in th 20 second range for me. That's on a dual core, 10,000rpm HDD with 4GB ram. The only upgrade I made to my hardware when I installed Win7 was a faster HDD and I replaced my 8 year old pci video card that I used for the 3rd monitor.
All in all a big win, and if you're a BizSpark member, you can get unlimited licenses for your startup for $100, paid after 3 years.
Couldn't be happier.