You may also want to limit things such as the number of simultaneous logins or disk usage. These aren't covered by ulimit; instead you should look into one of the following packages:

• Clobberd monitors user activity, and meters resources such as time and network activity.
• Idled can log out users that have been idle for too long or who have been logged on for too long. It can also prevent users from being logged in too many times, and refuse users from being logged in at all.
• Part 4 of the LPI 101 series discusses the implementation of filesystem quotas.