There are still a tiny fraction of vary good ideas that are worth something. Pagerank is a classic example where the idea was clearly worth something the problem is even great ideas tend to be worth less than 5% of the company after a year or so.

The hard part is sticking to your guns and actually telling your 'friend' that sounds like a good idea. You can pay me X/hour to build and market it or I can build it and hand over 5% of the profits it's up to you.