As you may have heard, NetBeans sources will be moving to Mercurial. Why is this happening? Well, CVS has lots of deficiencies and other Sun projects are migrating to Mercurial as well (OpenSolaris, OpenJDK, Glassfish). More reasons why are we switching are here.
Mercurial is a distributed versioning system (you can read more about distributed versioning systems here). If you are new to Mercurial or distributed versioning systems, our guys created great training materials. There is also a Mercurial plug-in available for NetBeans 6.0, you can get it from the update center (screenshots of the plug-in are here).
I really like the possibility to work offline with Mercurial. Our admins will like the fast branching options (I heard it can take 12 hours to make a branch of NetBeans CVS tree - isn't that insane?). Most operations will also get faster because they will be local. But there will be also some problems for sure - Mercurial is quite young and going from CVS to DVCS is quite a big paradigm change but hopefully it won't hurt too much...
Update: I just did my first push - how exciting! This wiki page is also very handy: http://wiki.netbeans.info/wiki/view/HgHowTos