Yeah - I think the real challenge for startups is often that the communities and audiences for what they do, particularly early in the game, aren't often well-defined. Even when they are, they are often fragmented, and the precise interest targeting in Facebook Ads only works for Pages above a certain size threshold (unclear what exactly this is) - so if your target audience likes a few dozen smaller, scattered Pages, you can't necessarily target them directly.

For some startups/companies, though, there is a pretty clearly defined audience, or a big competitor with an audience to target. If I'm Hipmunk, I can run ads targeting Kayak, Hotwire, Expedia, to go after people who I know book travel online (and then, of that subset of people, target only people who match certain demographic/geographic parameters).