This is of interest to those of you who (1) use Macs, (2) use Apple's X11.app, and (3) do not follow Apple's x11-users mailing list. (Which I don't blame you for: it doesn't generally have a lot of signal; I probably only read one message in twenty.)
This weekend has seen more traffic on the list than the entire rest of October. All of it complaining about various bugs with the new x.org-based x11.app on Leopard, including a couple of show-stoppers:
option-click no longer sends middle-click; nor does any other key-combination anyone has found (though 3-button mice are reported to still DTRT)
"Spaces is a total basket case with X11".
Apple's lead X developer has been active on the list all weekend, so they're paying attention. But I'm certainly not going to be switching to Leopard any time soon.