Apple's 0.2 version of their X11 beta has just been released. Looks like they've fixed a bunch of issues, and only a few things remain that are true annoyances as far as I'm concerned. The last version was too buggy for regular use, to me, but this one looks good enough to put into regular rotation.
Good job, Apple!
Update: Looks like they still haven't fixed the issue of 0,0 on the screen being above the apple menu bar. If you plan on using Apple's X11, plan on using quartz-wm or you can still lose your windows behind the menu.