At least as a preview release, in a nice easy-to-install package. You can get it from Jeremy Huddleston account on freedesktop.org: X11-2.1.0.pkg. Here is the (kind of hard-to-read) changelog since the bug-ridden 2.0 release included with Leopard. If you’d prefer to follow what’s going on in real time, the regular changelog is now on the git project page.
Also of note is that the main site for X11-related news on Leopard has now moved to http://xquartz.macosforge.org. The 2.1 package should appear there very soon.
Bloody Fingers 