Its odd, but I feel like I've seen this project (some sort of cancer killing thing) win at each of the significant science fairs over the last couple of years. From my experience, most of the kids at these high level science fairs just make reports over stuff they've worked on (not designed) in a lab.

My sister is currently working on a pretty good science fair project involving paint that can generate solar power. The cycle for this was to come up with an idea, email universities/labs in the area, find a mentor who agrees to work with them, and then just listen to and do what the mentor advises. Its still a great project and she is learning a ton from it, but not really something she designed and I wouldn't be happy to compete against it with something I came up with and made in my garage.

Overall, I wish there was some sort of limit to how much the mentors are able to be involved. I had a ton of fun (and learned a lot) doing $150 max budget, internet research only projects mostly on my own (sometimes had help from my dad building apparatus), but its pretty impossible to compete with people working out of labs with professional help.

Also, I just realized that some guy I met a few months ago when school started (and who I have classes with) won the Siemens competition last year.