UPDATE: This also applies to Windows 7 Final/RTM (7600) and will also work for the U820/U2010/U2020 models. Check my comment for additional information on what needs to be installed on those models.

I just installed Windows 7 Business Build 7000 on my U810. It is quite nice actually and seems to run faster than Vista.

I installed the Vista drivers from the driver CD. The Setup.exe on the driver CD will complain that the operating system is unsupported. To circumvent this problem, just start the setup in Vista compatibility mode:
Right-click on “Setup.exe”, “Properties” -> “Compatibility” -> “Run this program in compatibility mode for:” “Windows Vista”.

Install these items:

Drivers
04. Button Driver
05. Camera Driver
07. Fingerprint sensor (driver)
08. FUJ02B1 Device Driver (HotKey Driver)
09. FUJ02E3 Device Driver (System Extension Driver)
11. Pen Driver
12. Pointer device driver

Utilities/Applications
03. Button Utilities
07. Fujitsu System Extension Utilities

I could not get the Auto-Rotation feature to work. Also, you’ll probably have to calibrate the touch screen.
I also disabled the power management feature of the FCL USB Pen Tablet in Device Manager (Right-click on “Human Interface Devices/FCL USB Pen Tablet”, “Properties” -> “Power Management” -> Disable “Allow the computer to turn off this device to save power”). This improves the response of the touch-screen/tablet.

Oh, and BTW, Windows 7 “only” uses 7.5 GB of disk space, whereas Vista uses 15 GB I think.