root (0) - complete system control
bin (1) - historical
daemon (2) - all system daemons with user accounts
tty (5) - access to ttys?
ftp (11) - has personal ftp (~/srv/ftp)? Can control ftpd?
mail (12) - ability to use usermail (/usr/bin/mail)
log (19) - access to /var/log
locate (21) - ability to use locate
http (33) - has personal site (~/srv/www)? Can control httpd?
games (50) - access to games (/usr/games, /var/games, etc.)
lock (54) - access to lockfiles
network (90) - access to network devices (lan, wifi, dial-up, etc.)
floppy (94) - access to floppy drives
scanner (96) - access to scanners
power (98) - ability to control power state of the system (e.g. shut it down)
users (985) - default user group
video (986) - access to video hardware (used for FENIX display server?)
uucp (987) - access to serial ports and connected devices
storage (988) - access to removable storage (usb drives, zip disks, etc.)
optical (990) - access to optical drives
lp (991) - access to printers and parallel port devices
input (993) - access to input devices other than keyboard
disk (994) - access to block devices not in floppy, storage, or optical
             (this includes access to all hard drives)
audio (995) - access to audio devices
wheel (998) - administration; subsumes adm and log, has access to su
adm (999) - access to protected logs (i.e. kernel logs)
nobody (65534) - an unprivileged group