As of Nov. 2010, eMusic re-downloads are no longer free. It's still possible to re-download songs from eMusic, but you now must pay for them again.
The only exception to this is when the song has been removed from eMusic due to a record company’s contract with eMusic ending. In that case, you won’t see a listing for the song or be able to download it again.
Learn how to redownload songs at eMusic.