Puts incoming files in per-sender subdirectories of the default directory.
Source code available
If your Adium is configured to automatically accept files, things should Just Work. If you're prompted for the download directory, going with the default directory (the "Save files to" directory in the File Transfer settings) will cause the file(s) to go into a sender subdirectory. If any directory other than the default directory is selected, the file(s) will go where specified and not into a subdirectory.