I would hardly call seeing something on HN and wanting to make an app out of it a "great idea". I would call that, I don't know, not your idea at all. Windows still has 80% of the market-share on desktop, and soon droid will over take the iphone market. I think your thinking is backwards on a great many things. How about you find something you are passionate about, using technology you are already good at, and then try to "start".