Code on CVS is the latest working copy of the code the developers use, so right now for example CVS has the 0.99.4 work-in-progress code on it. CVS does not distinguish between stable and unstable releases, it's always simply the latest code, but if you grab the code immedately after a stable release, that's probably stable code.
Plugins don't usually change that much between stable/unstable builds; it's usually the IDE and runtime that are changing between stable and unstable.