To what end? Prefetch is aimed at... well... prefetching data and loading it into memory before you actually need it. Deleting these files would likely hinder it's efficacy, since it's likely using some kind of machine learning system to do more accurate predicting.
It's highly unlikely you'll cripple the system in any way, but it seems a bit like shooting yourself in the foot before trying to make a quick getaway.
With xp and vista I would delete the prefetch files under windows about once a month and it did seem to help. I have just got a computer with windows 7 64bit and was going to do the same. When I go to the prefetch folder I see a small lock icon on the folder, what does that mean? Is it safe to delete the files under prefetch like it was under xp and vista? I have search this under google but only find people that say to do it and then others that say it will only hurt the computer. Hope to get a better answer here. Thank you