I wrote a shell script that controls and logs your internet usage, hope someone will find it useful.

netctrl script: http://gist.github.com/187318

Basically you set up a cron job (use "netctrl -c") to take your computer online and offline at sometime automatically, and when you want to use internet when you are not supposed to, you have to specify a reason to do so (use "netctrl -u"), and the reason is logged.