Quoting from Parallels Official Blog Site:

Good news! We've launched the Release Candidate (RC) for Parallels Desktop! This release is a direct result of the awesome support from the Mac community...so thanks again to all of our 100,000+ beta testers. Upgrade to RC now.

Before I discuss the changes you'll see in the RC, I wanted to address the product name change. As you probably know, "Workstation" is a very Windows-centric term, and we recieved a lot of comments from our users stating that since we've got a great Mac product, we should make it look and sound like a Mac product. We listened, and the result is "Parallels Desktop for Mac". We're really pleased with the new name, and we hope that you are, too.

Now, onto the important stuff...what's new in Parallels Desktop for Mac RC? The answer is "lots." Check out the improvements:

* New look and feel
* Improved performance and stability
* Better and broader USB support
* Improved Shared Folder functionality
* Improved networking
* Better sound support
* Better fullscreen operation
* Resolved Suspend/Resume issues
* Uninstaller introduced
* National keyboards mapping issues have been fixed
* Red “Power Off” button now always acts like Power Off
* Blue “Pause” button now always acts like Suspend
* The “Pause” button was moved to the VM menu

As good as the RC is, there are a few known issues that we're resolving now:
* Some USB devices are still unstable
* FreeBSD 5.4 installation sometimes hangs

NOTE: If you are upgrading from beta4 or earlier, you will need to reboot after installing RC.

NOTE #2: You'll also need to reinstall Parallels Tools, regardless of which Beta you're upgrading from. You can easily do this by booting your guest OS, clicking the "VM" tab in the menu, and clicking "Install Parallels Tools."