As I just announced to the X.Org mailing lists (I'm the organizer of this year's event), the 2011 X.Org Developers' Conference is taking place in Chicago, Illinois from the 12 to 15th of September.
Initial details can be found on the X.Org Wiki
. For easy convenience of developers, it's falling the week after the Linux Plumbers Conference in Santa Rosa. (It's also falling right before Oktoberfest, in fact it ends the night before the start of the yearly Phoronix pilgrimage.)
As always, I'll be posting my notes from the X.Org conference on Phoronix. There will also hopefully be audio/video streaming.