It's been a little over a year since I posted the initial open release of the DTrace probes for the X server. I've gotten busy with a number of other things since then but after a little prodding from the JDS team , I've finally run them by the Sun Architecture Review Committee (PSARC case id 2006/609), got their thumbs up, completed code review, and integrated into our Solaris builds of Xorg & Xsun (which due to code sharing also means they're in Xnest, Xvfb, and Xprt). If they pass QA testing, they should appear in Nevada Build 53. I've also put them into the X.Org community git master branch, so they should be in Xorg 7.3 when it ships next May. (The autoconf code for them only checks for the dtrace command needed to build, not for the OS, so when MacOS X & FreeBSD users get DTrace, they should be able to build the probes as well.)
I've also updated http://people.freedesktop.org/~alanc/dtrace/ with the few changes made to the probes since initial release (added an event probe, and changed one of the arguments made available by the request-done probe) and to include a patch against the Xorg 7.2.RC1 tarball for the current state of the probes for those who don't want to wait.
 The conversation went something like this (slightly paraphrased):
jmr: Yes - and what about the XServer dtrace probes ;)
me: oh, um, well, yeah, okay...