I was surprised about they did not present it at the keynote, i consider it as a big important step. X11 is working sweet taking advantage of the quartz rendering now.
anyway you can get more infos on the following websites: http://www.ppcnerds.org <-- they have a news and some good links for the apple X11 http://www.opendarwin.org <-- they are part of apple members working on the open-source side http://www.xdarwin.org <-- another good project
I agree, integrated X11 promises to make thousands more apps available to ordinary OS X users. I really hope Apple add virtual desktop support to the OS X desktop. If you haven't used virtual desktops you don't know what you're missing, they are one of the best features of X11 window managers (like Window Makers and FVWM).
For example you could keep photoshop open on one desktop, a web browser and text editor in another, etc. Allows you to quickly switch between desktops laid out and ready to use. No more minimising and unminimising all the time or cluttered desktops.
Virtual desktop wouldn't be hard to implement and it can be an optional feature for those who prefer one desktop.