And the '10-user' vs. 'unlimited user' licenses only refer to using Apple's tools and AppleTalk. For the underlying UNIX tools and networking protocols, it's 'unlimited user' even on the non-server edition of OS X. (So, for example, the 10-user license will limit a server to allowing 10 clients to connect using the 'afp://' style, but unlimited using the 'cifs://' style; or unlimited web connects, SMTP, etc.)
Yeah, there are decent tools for 'server' functions built into the non-server version of OS X. If all you want to do is serve up files, though, getting a 'Net Disk' might be better. (An external hard drive that has USB and Ethernet ports.)