@rango: the way I understood the low quality comments by JohnMu and the entire discussion around the subject is not so much that the low quality pages don't rank well themselves - I assume Google already knew how to prevent them from ranking long before Panda 21.5
I understood the problem as a certain amount (perhaps percentage-wise of the total indexed) of low quality UGC brings THE ENTIRE SITE down, no matter what quality the other pages are. The path he'd suggested seems logical but it could only possibly work if Google ran the same type of update once again after you've no-indexed low quality UGC. I have a very dim view of our chances to see this one-off update be ever run again. I don't believe it has achieved the result they wanted and therefore there would be no reason to run it again. For all we know, they might have simply abandoned this entire branch of anti-spam research that was specifically aimed at UGC sites.
I would add that if the page with UGC had attracted ANY outside links whatsoever (in a natural way, of course) , then it's likely by definition no longer low quality, no matter what the pages actually say. So there would be no reason to no-index it in the first place.