I was looking at credence, and it has four big problems, imho:
1- It's dead (or at least appears to be)
2- The users have to finish the download in order to vote. This doesn't make much sense since it's possible to preview the files.
3- It relies on sha1 to vote. The sha1sum of a downloaded file isn't the same sha1sum of the same file ready to download, because of the bogus SHA1sum.
4- A bad named file would give the users that voted thumbs down a worst "karma", and therefore getting more spam.