Cleaning out uploaded files

I'm building a printing site based off ZC. Every product requires one or more file uploads. HUGE ones, if you think of a printing site.

I would like a way to be able to go in and clean out files that aren't being used. Say a customer uploads a file and adds a product to the cart, then goes back in and uploads another file to replace the original. Or deletes the product from the cart. Basically anything that will cause an uploaded file to no longer be associated with a customer product.

If there's no existing ZC way to do this, I can custom-code it. I'd appreciate pointers on where to start, though. Any advice on what tables I'd need to check to make sure I'm only deleting "orphaned" files? It seems like it would be easier to do this in one place than to try to find everywhere in ZC where a file could stop being associated with a product, but I'm open to any suggestions.

I have a bad feeling that this site is going to be VERY quickly filling up my client's disk space! :cry:

There may also be server restrictions on the size of uploaded files - unless you have your own server...

I have my own server, so that's not an issue. And I know I'm going to have to come up with some way to archive the older files that ARE being used at some point anyway. But I figure a good start is to be able to delete the ones that aren't actually being used for anything.