Not sure for ATI/AMD GPUs but for Nvidia its quite glitch and crash tastic. I would wait until Doh gets her hands on Lion and Apple starts posting the source code for their xQuartz implementation (if I remember at a main release the sources tend to be quite behind until Apple updates the public source code and the community tends to fix stuff from there with Apple's maintenance update being mostly catch-up with the public code). That and Nvidia GPU drivers get updated.
Apple is always way behind in X11, even in new OS releases... so thats not an issue, XQuartz is already working decently on Lion. Wineskin is running fine so far on Lion... STO and some other games are having problems, but it seems to be due to faulty graphics drivers on Lion... eventually they should be updated to fix issues.