(Sorry for the inconvenience)
As of September 2008, PC-BSD release version numbers are the same as those for FreeBSD. When the first number of a release is followed by a zero (e.g. version 9.0), this means that this version of PC-BSD introduces many new features. When the second number of a release is not a zero (e.g. version 8.2), this means that the new version may have some new features, but it mostly fixes known software problems and security vulnerabilities. If a release includes the letters RC, this means that it is a "Release Candidate", or that the developers are still adding and fixing features and need testers to help them find any existing problems in preparation for the upcoming release. If the release includes the word BETA, it means that that version is still buggy and needs the help of testers to find as many problems as possible so that they can be fixed.
NOTE: if you want to use PC-BSD (not test it), you should install the most recent release (i.e. the one with the highest number), not a BETA or RC version.
The change logs for each PC-BSD release are available: