I rebuilt my machine due to system instability and decided to go with Windows 7 x64 this time now that we have a release candidate. So far, this is running much better than Vista ever did and some of the new features are compelling. I think my favorite feature so far is how the window manager groups related windows behind the application icon only, and--wait for it--lets you CLOSE them from the window preview when you hover over the icon. You no longer need to raise the window first and use its close controls or right-click to close-the 'x' icon is right there on the preview. This seems simple, but it's a great improvement.
Another nice feature is the selection of a wireless network. This works the same as Ubuntu does now and just shows you the available networks with a single click. Each has radio buttons to select it. No more wading through multiple screens just to change networks.
I have hit one bug: I have files on my desktop (as shown in \Users\user\Desktop), but the desktop itself is completely clean. I can right-click on the desktop and create new files, but while these appear in an Explorer folder pointed to that location, they vanish from the desktop itself. Has anyone else run into this?
** Update: I'm an idiot; it's a setting to show icons on the desktop. I am not sure why this was off by default. The setting is under Control Panel\Appearance and Personalization\Personalization\Change desktop icons, and you check User's Files.
Overall, I highly recommend giving the RC a spin.