I hope no company will make their decision just because a candidate says that he is an excellent developer ;)
Technical interviewing in a broken process. I've given almost 200 technical interviews at Google, and I've seen all kinds of results. But, I believe Google's results. Having worked at Google longer than anywhere else I've ever worked, I can say that the people are incredible, and it's a direct result of the interviewing process. We interview someone for a set number of interviews (Nā¤8 nowadays) and we make a decision. I can count on one hand the number of people I think are deadwood.
All I'm saying is the "interview" process of having people do projects for you is broken. You will filter out a lot of people with jobs they are kicking butt at.
Also, who says "I am an excellent developer"?
I am an excellent developer, with years of experience in the industry. I know lots of technologies, and already have a great job. There is no reason for me to spend personal time writing your projects, when I would be rewarded by spending personal time on my employer's projects.
"Interviews" like this will only grab candidates with nothing better to do than to fulltime interview with your company. In my opinion, the best people already have jobs, and you're excluding them from the process.