A little harsh on newbies or people without guilds, perhaps, but understandable considering no-one likes to wipe continuously due to someone not knowing what to do.
However, I was LFG for Emalon 10man the other day when the following conversation occurred:
Apparently, having the Achievement for 25man Emalon just isn't enough for 10man Emalon.
With such a stellar raid leader, I wasn't surprised when the PuG failed, mainly due to one of the tanks getting flattened within a minute for some reason... he wasn't undergeared as far as I could tell, but he must have been missing something crucial somewhere.
Luckily I was able to join another (successful) PuG after defending Wintergrasp. I would have been incredibly annoyed if I'd been locked!