I used to do per project fees exclusively but I found that with certain jobs, mainly ones that involve a lot of drawn out unpredictable grind (like repairing broken circuit boards), hourly is much better for me. Different situations call for different solutions. I still charge per project for jobs that don't lend themselves to being measured with clocks. Oh, and just FYI: not all freelancers are programmers! In fact, some people do work that doesn't involve computers at all. True story.