After two years and two ideas that failed, (executed poorly, no traction, no market, trouble in cofounder paradise -- you name it, I've failed it), I decided to try a different approach: rapid exploration of niche products. In the course of a year I spun through about one idea per month.
I got remarkably good at (in)validating my ideas. (Hint: write down who you think your target market is and then pick up the phone. Have a conversation. Ask if they would pay $X dollars for your product where X is something that makes you cringe because you think it's too much. If it's worth pursuing they won't hesitate to say yes. Then tell them if they give you $X right now you'll start building it for them -- if they ask where to send the check you're golden, otherwise you need to rethink your assumptions. If you don't know anyone to call run some ads to a fake landing page, collect emails, then offer an amazon gift card or something for a 30 minute phone call. I wrote about it here: http://twosixes.wordpress.com/2010/05/29/tips-for-talking-wi...)
I finally landed on something, (and feel free to steal this) -- filtered google alerts for PR agencies. I had customers using the service and waiting for a bill. But I never implemented the billing system, I procrastinated it hard core. It wasn't because I was afraid they wouldn't pay, (they would have). It was because I was afraid of supporting the project. It was like I built myself a job I didn't want.
So for me the biggest pitfall of this approach was a total lack of vision combined with a drive to pivot to product/market fit at all cost meant I created something I had no passion about whatsoever.