Sounds like a good idea. Though the download numbers might not truly reflect popularity since one often has to download something to decide if it's useful or not. I end up discarding many things I download when they end up being of no value to me.
Another idea might be to offer the ability for users to rate files, either numerically or something ala amazon.com's "Was this review helpful to you?" feature.
Any rating system would help us figure out which files are most useful though.