Renaming of files just like in the Micrososft Office Picture Manager (this program can`t handle psd) would be great: There it is possible to add something to the current name (up front or at the end), for example.
By this you don`t lose the current name and the infos stored in it.
Sometimes I get duplicate file names because I import from two different cameras. I have to manually rename and then re-import these photos. It's an even bigger pain when trying to merge photos into one folder. I wish Lr had a renaming system similar to how Windows/Mac ask you if you'd like to rename a similarly-named file when moving.