you can have two /etc/hosts (hosts - hosts.restricted), and a script switches each.

implementation is left as an exercise for the reader.

If you have TextMate and want to be able to disable and enable those /etc/hosts lines quickly, see the Screenr HOWTO:

  http://screenr.com/Sg7

After seeing Alex use Screenr, I just had to try it out myself.

short version:

  1. mate /etc/hosts
  2. select the lines you want to comment out
  3. command forward-slash (⌘/)
  4. save and authenticate if necessary

You can write a slightly more complicated index.php than he does to time how long it's been since you last checked a distraction, and give you an allowance of, say, one distraction per hour. If you're allowed, the script can just proxy all requests for half a minute.