Looks like the people that are still running the Windows 7 Beta are feeling the effects of the kill switch installed by Microsoft. The new "feature" was activated today and will shut down your system every two hours just to annoy you into installing the Release Candidate.
Of course once you do install the RC you can expect to be visited by the shut down fairy in March and to continue to have a two hour work time until you pony up for the full product.
This new technology was installed through a series of test updates that no one could ignore. It is rumored that this will be part of their new piracy protection features, and could kill any non-legitimate versions of Windows 7 that the activation servers detect.
Windows 7 is scheduled for release in October and has been gaining in popularity as many are still leery of Windows Vista.