This is an old one, but for those of you who didnt know about it: cancel all your plans for the next few days, get a bunch of food next to the computer, and prepare to vegetate http://www.addictinggames.com/helicopter.html
When i lose i'll always think "Just one more try, to see how far i can get" or "oops, gotta try again, stupid mistake" or my favorite "that shouldnt count, one more" I get consumed for hours