Well, this didn't seem to bother investors since they've just raised $10m. They've got enough cash to figure out what'll come next if Facebook comments gain too much market share.
Very thoughtful piece, thanks a lot for sharing this. It seems so far that M&A valuations are following up serie A valuations (see Google & Path for instance). The bubble, if it exists, is no longer limited to the seed ecosystem.
Big brands like P&G have begun buying lots of Facebook ads, and they seem quite satisfied with the results of their campaigns (at least satisfied enough to ask for more...).