Startup idea is important, but the only thing that matters is execution. So probably there is no point to protect the idea unless it is something revolutionary.
Many successful projects do not bring any patentable IP although perfect execution makes them winners.
There are examples in both product and social media areas that prove it. After all, Evernote is nothing but a notepad in a cloud. No revolutionary ideas here and yet the business is worth billions. Execution matters.
