Ask HN: Deciding between microISV and something bigger

I'm looking for feedback, pointers, anecdotes, etc. I started building an iPhone app (one that is actually useful) with the thought of making some extra money. As I've thought about it, I've thought of some ways that it could be expanded with a web presence.

The question that I have is this: How do you decide when an idea is "big" enough to justify really "going for it." Or is it a function of people over idea (e.g. the right people can make a go of most any idea)?

I'm still slugging away on the original idea (don't want to get distracted :), but I'm sitting with ideas that might be worth pursuing.

Also, FWIW, I don't have the advantage of being single with no kids and no mortgage, so turning in a YC app isn't really an option. You whippersnappers have it so good these days.