This is a really nice post from Ben Byer at Apple on the changes to X11 in Leopard.
I found it after going to look for the solution to the same annoyance that others were having, namely that my ~/.xinitrc seemed to be ignored and launching X11.app would create unwanted xterms (have I mentioned that I really HATE xterms?)
Anyway, the new launchd implementation of X11 is great for me. In order to use terminal.app or iTerm with X11 in Tiger I had this whole block of an if statement in my bash profile that would open /Applications/Utilities/X11.app – and then run osacript to bring the focus back to the Terminal, but only do it for console terminals, not ssh terminals, and set $DISPLAY right, and…. and it was just a kludge.
I love the fact that I can ssh -X now and it just works.