MP3 Uploading Question

[eluser]matt6805[/eluser]
I've created a simple site where users can upload mp3 files to a directory for others to listen to. The mp3 file contents are checked by the admin before they're published to the live site.

My concern is the upload feature. Although I've limited the file extension to only allow MP3's, are there security concerns I should be aware of before I make this live? What's the best way to protect my server and users from malicious files being uploaded? Thanks all!

Regards,
Matt