Bazaar has been a great productivity booster for me lately. It enables me to work on several concurrent major refactoring tasks, and painlessly merge between them. You can imagine what it would be like to do several merges daily with SVN or (*shudder*) CVS.
The biggest new thing I'm currently working on is the Box2D integration. I'd estimate I'm about 40% done now, and the biggest obstacle has been (once again) having enough time to code, but I hope to have the main functionality + a simple demo working next weekend or next week.