As long as they aren't rude or something, I will tip on take out orders. Not as much as if I was actually sitting in the restaurant being waited on for an hour, but still something.
They still had to bag it all up and bring it to me. And frankly, I worked in tipped jobs for many, many years and that unexpected tip can turn a really REALLY crappy night into a good one. I figure its worth the $5 or $10 or whatever to possibly turn someones night completely around.
I know there were several times when I was having a REALLY bad night (and I worked in strip clubs for awhile so bad nights could be REALLY bad).... No money; we worked ONLY on tips alone PLUS had to pay a house fee, DJ fee, etc... to work every night so if we made nothing we could actually leave in the negative. Rude customers trying to grab on us for free or telling us we weren't worth spending money on because we were too fat or too thin or not blonde enough (whatever excuse they could think of to cover the fact that they just didn't HAVE any money).
And then there's one really awesome customer who would stop on his way out and say, "Looks like a really crappy night for you girls. Here...maybe this will help," and give each of us a $5 or something. Had a guy hand me $100 once because, "You are too pretty to look sad, even on a night like this."
I believe in karma. I believe in passing it forward. I remember each and every customer that turned a horrible night around for me with their kindness. Therefore, I try to do the same whenever I can. Whether its technically "right" to tip for certain things... I know how much a couple of bucks, and just the gesture itself, can mean to someone.