Don't worry about it, ideas are a very small part of a successful business. Apple wasn't the first personal computer company, Ford didn't build the first car, McDonald's wasn't the first hamburger fast foods business and Google wasn't the first Internet search engine. Do what you're trying to do well, give your customers value for their money, and don't break the laws on intellectual property.
I've written about this several times on my blog "Up and Running" here at Entrepreneur.com"Ideas are Easy, Doing Stuff is Hard
Also, you'll like this one, on my Planning Startups Stories blog: Second or third mover advantage
It's answering this same question, although it was a while ago ...