1 - To me file duplication is not necessary. Don't ever do that. Lazy uploaders will just copy your file and save it into their own accounts. Please don't implement it.
2 - Mass renaming is one of the most important factor I look in a file host. Imagine you have 100 over files to rename, it would be a pain in the ass to go through it one by one. And trust me, uploaders usually have more than thousands of files.
Rapidshare, Hotfile, MegaUpload, MegaShares, DuckLoad, Filesonic, Fileserve (coming soon in their new file manager) and a whole lot more. You should take a look at Fileserve's thread and see how many users suggest mass renaming.