The X.org Wiki has [a page](http://www.x.org/wiki/XDarwin) for updates for XDarwin. I was still having some issues (with `CURSOR`) that these updates fixed. The two lines that will do the updates are:

curl -LO \
http://people.freedesktop.org/~jeremyhu/x11-apple/x11_update.sh
sudo sh x11_update.sh

UPDATE: it appears you should get your updates [here](http://trac.macosforge.org/projects/xquartz) now. I still have X problems, but things are definitely improving.