Working in the 'online world', it is hard to not have multiple ideas per day on things that you would like to create. More than anything else, what I have learned is that execution is all that matters.
Shipping is vital. It's not the only thing that matters, but getting your idea into something that people can interact with has to be your number one goal. How you execute (along with some or the random market stuff) will determine how successful your idea is, but you can't know how well you execute until you actually do.
I've thought this many times, but I'm writing based on Brad Frost's recent release: This is Responsive. I had an idea for something like this and grabbed up a domain (responsv.com) for it. I had an idea, but I didn't take action.
The great part is that the world now has a site like this. Brad has put in a ton of work on it already and it is going to be fantastic. He did some really cool stuff like putting lots of code samples on Codepen. He has a lot of swagger in the responsive group, so I think it is probably better to have someone like him behind this project. I love seeing the great reaction and the numbers on Codepen because it confirms that I at least have ideas for things that people will dig.
That is good and it is getting me moving on my one idea that I haven't been able to kick out of my brain for the past year.