Playing with Windows 7 the last few weeks, I've found that my laptop refused to wake from sleep. The display alternated between not even powering back on and powering on but remaining black with a non-responsive mouse cursor. The only way to recover was to hard-power Lappy off and back on. This seems especially prevalent on Intel 945 chipset displays.
The only workaround I've found for now is to turn off sleeping completely and instead use hibernate. I've had no problems powering back on from hibernate so far, it only takes about 20 seconds to do with Windows 7 on my system, and doesn't drain your battery like sleep does.
The updated Intel 945 driver released today through Windows Update did not fix Wake From Sleep yet. Hopefully it's an issue that will be addressed before RTM.