Tonight I'm merging a bunch of changes from me, Britton Smith, John Wise and Stephen Skory back into the trunk from the mercurial repository. If you're running on the yt-1.5 source tree, this won't affect you -- but if you're running on trunk, the next time you update you will have to rerun "python2.6 setup.py develop" or "python2.6 setup.py install" depending on how you installed. If you used the install script, you should also be able to re-run it at any time to get an updated source tree and installation.
There are no pressing fixes in this, only speed and memory improvements, so don't feel it's necessary to make the jump just now if you're happy with where you are. If you do update, here's a minor changelog:
All the public and primary functions, classes etc should be the same.
Thanks, and let us know if there are ANY problems!