The Windows 7 craze started early last year when the first public beta of the operating system became available. Then in May the thing took an enormous momentum boost with the first and only release candidate that saw the light outside of Redmond. Today I keep running RC1 on my main workstation and a couple of laptops in spite of having bought licenses for all those machines months ago. For some reason I tend to believe I'm not alone in this situation.
Microsoft has issued a reminder that in two weeks users will start to see notifications in the taskbar once per day with further notices presented through the Notification Wizard. Then on March 1st the release candidate will start taking automatic reboots every two hours. Officially the RC license expires on June 1, 2010, by which time you will be treated with some "non-genuine" prompts and refused of your wallpaper among other things.
If you haven't moved to the final code yet, you should start planning the migration soon and skip the trouble. Unfortunately there aren't as many Windows 7 deals around anymore and Family Packs seem to have gone the way of the dodo.