A few changes have been made since the first Release Candidate, and the final release will probably be next, so it’s time take it for a spin and try it with your favorite plugins and themes if you’re concerned about compatibility.
If you run in to any problems, please feel free to discuss them in the Alpha/Beta section of the Support Forums or contact the wp-testers mailing list. If you run in to any bugs, please follow this guide to report them.
Have you tried WordPress 3.1 RC2 yet? If you have, what do you think so far? Are you ready for the final release of WordPress 3.1?