I use a combination of git and Subversion. SVN for the main repo that is shared between developers (with many developers working at once the lack of atomic commits really sucks), and git as my own offline versioning system. The code that I write tends to go through several iterations, and I'm loathe to commit anything to SVN until things work well enough to please me. Bad code should never make it into your prod repo, but I'm not a fan of rewriting/deleting mass chunks of code without SCM to back me up.
Ok, this convinced me to at least give git a try. I made the move to SVN from CVS years ago to be able to rename / move stuff in the repo, but the offline version control would keep me from keeping a bunch of updates in a branch uncommitted while I do a major push.
My current offline version control system has been leaving all the files open in TextMate to take advantage of undo/redo. (Horrible I know).
If you just want the offline aspect, you can use svk (http://svk.bestpractical.com/view/HomePage). I also switched to git for that (and stayed because I liked it better in a lot of other respects), but I found out afterwards that you can use svk to use svn offline.
