I just realized one big thing that Freckle and Stack Overflow have in common: they have virtuosity built into the definition of their target market.
Freckle‘s target market is defined as small businesses where everyone trusts everyone else. That’s how it can be a social time tracking where everyone can see everyone else’s entries. And tagging makes seeing other peoples’ entries useful for owners, managers, and employees alike.
Stack Overflow, on the other hand, is geared mainly towards programmers who want to cultivate knowledge. It’s also geared towards google searchers, but they’re not the core group, and don’t get the benefits available to the core group, like reduced advertising and moderation abilities.
For a counter example, there are mass-email companies that sell their servers to spammers. And there are ones that avoid spammers, but have a hard time achieving separation just by how they define their target market (and saying people who want to send mass email minus the spammers doesn’t work well). But Campaign Monitor circumvents that problem by marketing to designers, who are an intermediary between them and a larger group which includes spammers, that keeps most of the spammers out.
I think defining a good customer base is a large part of having a good customer base.