If you are still running any of the BETA versions of Windows 7 you could be in for a surprise come August 1st. It looks like that is when the BETA versions will expire.
For those using the Release Candidate you have until June 1st 2010 to enjoy your free copy of 7. After that it is up to you to move a "different" version to keep using the new OS.
Read more here.
On June 1st your Beta will begin shutting down your PC every two hours and we are sure that this will be very annoying.
It is up to you to upgrade to Windows 7 release candidate one that will run your PC until June 1 2010 and after this date you will have to get out and buy Windows 7. At this time, there is no indication about the real Windows 7 pricing but you can at least hope that an upgrade from Windows Vista Ultimate should be cheap as people were more than annoyed with endless problems which Vista caused.