Well if I was going to do this here are somethings to consider:
1. You would have to decide what each user could or could not do or use.
2. What programs would be available to each user.
3. Amount of disc space, memory, and cpu usage for each user.
4. Would you offer Email. (IMAP, POP, SMTP)
5. Lock down the filesystem.
6. Back-up Stragey.
7. What type of "user" or "fair use" agreements will you use.
Just some items to think about if you are going to set this up. Also I could be way off base but you never know.