How often are SMP maps automatically saved?

I actually wrote a script to handle starting, stopping, console commands, and auto-saving on my Linux servers. I then have a cronjob that issues a save-all command every hour and another that backs-up the world to remote storage every hour so i can restore when my dick friends mess stuff up. I can do stuff like this from a Linux shell:

$ minecraft_server stop
$ minecraft_server start
$ minecraft_server_command [any server command]

Also using this script, I wrote a web application that I can interactively give myself (or whoever) any number of a resource (i.e. >64 at a time).

I'd be happy to put it up on pastebin or something if somebody wanted it. It requires screen be installed and the web-app is written in python with a django web framework and MySQL database so that would be kind of difficult to port.

If our experience on Fosco's server is worth anything: by far not frequently enough. We've easily lost hours worth of work due to server crashes. :(