You can patent an idea as long as it is sufficiently unique and no one has done it before - you would patent the "process" rather than the design which is covered by copyright rather than patent. Worth noting that patenting is a long, hard and frequently expensive process and some people believe that simply getting on and do it and capitalise on the idea as being first to market is better way of spending your time/ effort than months/ years of legal arguement.
Technically, you can't actually patent an idea - what you can patent is the process involved in making the idea work - which is where the writing of the patent is crucial. Chances are unless you have a unique technology you have zero chance of patenting - you could apply Trademarks / Copyright instead - it would probably give you more protection anyway.
Couple grand to get a patent, 10+ grand in enforcing a patent, someone finds anything that predates your patent, your screwed. I agree with being the first to the market. Up until 4-5 years ago you could not patent any type of software/internet app, or at least it was very hard so companies just encrypted there code, "trade secret". Then the patent office said sure why not, and gave patents out like candy. Sites like friendster now have a patent on any types of social networking sites, 3.5 years after they applied for it and there website had basically died. I saw one patent that a guy had that covered any sort of geographically advertising online, he will now try to sue every search engine who ip decodes to serve ads, come on. Since patent office moves so slow, and internet age move so fast, patents dealing with the internet actually could halt innovations, which is the exact opposite of what a patent is supposed to do...