The Windows 7 Release Candidate is available for download "free" (see previous post). In Microsoft terms, Release Candidate (RC) code is code that we think is ready for release to our customers but we are still doing some final test and evaluation before the official release. Installing RC code is a good way to become familiar with a product before it is released (RTM or Release to Manufacturing). RC code is usually very stable and feature complete.
I recommend you give it a try. I have been running Vista since the earliest internal betas and had no issues with the product. My coworkers kept ranting and raving about the new build so I took the plunge last week and performed an in-place upgrade. WOW! There is a noticeable difference in the day to day performance of my laptop plus a number of cool new features.
More information can be found here.