CLAMP-NET has been re-opened. It's trimmed down from the last website and now has a craft-like quality due to the photos of the clay figures and handwritten-like font, but it's pretty cute and the schedule calendar is useful. There's a facebook link, too, but it's down at the moment.
BTW, the xxxHOLiC drama blu-ray/dvd will be released November 6th. CLAMP will illustrate the limited edition box. More info here.