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