To expand and perhaps refine what Corey said . Before you read Lean Startup, and make the same mistake many people make (and I've spoken with Eric about this), which is to think he meant "plow ahead with any idea you have", read the following books:
"Just Enough Research" by Erika Hall
"It's Not Rocket Surgery" by Steve Krug
The first few chapters of "The Four Epiphanies" by Steve Blank
Then read Lean Startup.
Doing customer research and interviews is close, but you'll fall into the same potentially fatal pitfall as if you just do focus groups. These give you bad data. Asking "do you like this?" will generally return a "Sure, you did a great job" reaction -- lots of false positives, and you'll never ever learn what you don't already know.
Agreed with Josh in that you (as so many do) have done it backwards. Every line of code you write limits your ability to iterate or make large changes (what if your idea is of use only to you?), and more costly.
I always ask startups: "What problem does this solve, for who, and how do you know this?" All are important. And sounds like you can't answer this at the moment. That said, it might be something really useful for a lot of people -- but it might not be, and you don't know. Go find out, now.