Hey andiv83,
I purchased a u330 last month and upgraded to windows 7 64bit right away when I got it. So far I am very pleased with how windows 7 operates on this computer. This thing just screams when performing any operation and uses a relatively low amount of system memory.
There are some things you have to take into account though and you have to remember that the experience won't be quite "perfect" yet. But come the full release, all should be solved, I have no doubt.
There are currently no "windows 7" specific drivers for the u330 currently for download from lenovo's driver download site. http://consumersupport.lenovo.com/en/DriversDownloads/drivers_list.aspx?CategoryID=16
There are many vista drivers that will work with windows 7 though. Most all will work except for drivers such as Veriface (which lets you log into your computer and lock/unlock files by scanning your face with the webcam), switchable graphics driver (which allows you to switch on the fly between power saving integrated graphics or the discrete ati graphics card), and the lenovo power management system (there is a basic power management system available, but lenovo's management software is more specific to the u330 itself)
You can still switch between integrated and discrete graphics of course, but you have to do so through bios when you start your computer instead of switching on the fly by right clicking your desktop and selecting the switchable graphics program.
Currently I am running the ati discrete graphics, which provides less battery time of course, but I have no doubt once the full release of windows 7 arrives Lenovo will provide windows 7 specific drivers for the u330
Other than that I would say that I am very happy with my experience so far on windows 7. It definitely fits the sleek, sexy, and simplistic style of the u330!
Hope that helps in your decision