It's up to you really...
See what the development team have said about a release on their website... Do they maintain a labeled 'stable' release?
Most companies I've worked for won't install any updates until they have been available for X months...
This lets other users find the bugs, and upgrade a bit later!
Some companies I've worked for won't install the latest release at all, and deliberately stay one release number behind development.
If you're an end user (not an enterprise user) I wouldn't worry about it too much, just don't build your software from CVS or SVN repositories (most chance of being unstable as it's still in development). You'll soon know if the software you've installed isn't stable, then you can just downgrade.