If FMSA is the only thing we are using our server for, is there any need to buy the unlimited Apple OSX Server license, or will the 10-client version do the trick? We are authenticating against Open Directory on the same box, and have more than 10 users in OD. However, there are only 3 local accounts on the Apple server. Thanks for any info.

No problem, the limit of 10 clients is only used by the afp-service (Apple-Fileserver).

All other services (mail, smb,etc.) are unlimited. I think the background is, that most of the parts of MacOSX-Server are open-source (samba, postfix, cyrus,...) and only the afp-services are really owned by Apple Computer.

If you don't want to use the Apple-Filesharing for more then 10 users, the 10-clients-version will be ok for your needs.