I sorted the comments by oldest first and skimmed them looking for people dumping on facebook with things like "flash in the pan" or "i could build this in a weekend".

Surprisingly few. In fact most people loved it. So if you're looking for indicators of startup success they'd go something like: 1) 85% of target demographic has signed up. 2) 3.5 millions users. 3) TechCrunch commenters love you.