The maxusers variable has nothing to do with the number of user allowed on a system. It's one big knob that scales a number of other parameters simultaneously. The standard settings and derivations are more or less as follows, using /etc/system syntax:
* The big knob, scales automatically set maxusers = <amount of available physical memory in MB>* Maximum number of allowable processes; currently at most 30000 set max_nprocs = 10 + 16 * maxusers
* Max processes per user (5 are reserved for the super user) set maxuprc = max_nprocs - 5;
* Number of quota structures (need one per user per filesystem * w/ quotas) set ndquot = maxusers * NMOUNT / 4 + max_nprocs
* Maximum size of the directory name lookup cache (DNLC) set ncsize = 4 * (max_nprocs + maxusers) + 320 set ufs_ninode = ncsize