CueDB is an open content database, so anyone can upload a cue sheet for both music and data files. All you have to do is register.
When it comes to uploads there is basically one rule: DON'T UPLOAD CUE SHEETS FOR ANYTHING COMMERCIAL (CDs, DVDs, etc.). I want to make it loud and clear - if you do you will get banned.
Downloads are available through the website and client applications. The database is open so you can download anything even if are not registered.
The only thing I ask is that you keep the cue sheet intact when posting anywhere else (forums, etc.). I especially mean any comments added by CueDB/the author/the submitter.