Hi all! I know this thread has been quiet since yesterday, but someone brought it to my attention. I'm actually the Community Manager at GameSprout and I'll be happy to answer any questions you actually have about it if you're interested. (Just a warning that I'm out of the country and not at my usual office desk, so I might be a touch slow in doing so compared to my normal response time.)
To address the concept: it's totally true that most people say "the game idea by itself is worthless." But there's a lot of reasons why we're trying a different approach. For one thing, the people who have "that great game idea," but just aren't sure how to get started making it, aren't really going to stop existing just because their idea is impractical. I'm sure people who develop have all heard "I have a great idea for a game..." at some point. A lot of times people just aren't sure where to get started, so one of the biggest roles that GameSprout serves is that of education - helping people to refine their ideas, and letting them see just how much it takes to actually get a game made from a small idea. Even people whose ideas aren't getting voted up get the chance to see games made in real-time and the discussion that goes on openly about those concepts - discussion that might frequently occur behind the scenes in a more closed project.
As for other questions, skilled programmers or artists can volunteer their time, but we also have full-time game devs working for the site providing content to the top-voted ideas. This doesn't mean we'll work on every idea on the site or that every idea we work on will become a full-fledged game, but it does mean that people can see what ideas get traction, what ideas aren't fleshed out well enough to actually make, and what ideas turn out to be fun or not-fun after being prototyped.
On a personal level, I find this project really exciting!