RapGenius is a bad example. Their product (crowdsourced lyric annotation) obsoleted other lyrics sites almost immediately. That they had to play the dirty SEO game is unfortunate, but not surprising, given that they were competing against a field of even dirtier sites.

Klout, on the other hand, offered little more than reputation snake oil, which is why few take them seriously and the investors are lucky to be leaving with the shirts on their back (which is what a low nine-figure sale means). Much like Quora, there was a focused bubble of intense love, with a very long tail of disdain outside. Except Quora has a purpose.