In reply to Dan Lane:
Yep. The one that seems to be working at the moment, though it's not strictly a critique group, is the 'pictures you've taken this week' thread.
There have been flickr groups for UKC members for this, and the weekly photo crit group you mention, which did last for a good few weeks.
It's not that relevant for me because a) I don't tend to photograph climbers, and b) I'm a film photographer so I move at a snail's pace, but I still think they're interesting threads when they do appear.