Site should set a cookie on user's machines... way easier...

Another suggestion:
For bandwidth's sake, allow external linking.
For instance: I uploaded a them today, but I actually had to upload the file. I still host it on my personal site, and in the sites tables you could add a field "link" or create another table with as many urls as needed that provide the files.

table theme: id, title, description
table links: id, id_theme url_theme

So you could have as many mirrors and relieve LS.net's bandwidth!