XQuartz 2.7.7 on OS X 10.10.1 Yosemite
As I didn't have a lot to do this afternoon, I decided to check on the state of X11 on OS X 10.10.1 - and it's actually not bad at all. I was able to get Quartz 2.7.7 from the download site, and it installed easily enough. All the normal things run, and it's a complete X11 we just need the apps - or in the case of SSH access, getting to a linux machine for the X11 apps on the remote host.
Because I got rid of my home machines with X11 a while back, I'm not sure how much this is going to get used any more, but it's nice to know that it works before I really need it, so that I know I can go to it in a time of need.