Today’s the day that the pre-release versions of Vista before the RTM (january 2007) will stop functioning.
The Customer Preview Program versions of Vista stop working on May 31, this includes Vista Beta 2 and both release candidates.
Starting Friday you can only log on for about two hours. After that Vista will automatically reboot without giving you the chance to save your documents and other stuff.
What this means is that you have about two hours to get all your stuff from the computer onto another media/computer. It’s a short period, but it’s doable