Also, for delivery, there are often delivery fees. The delivery fee's are only partially dispersed to drivers. But, then again, I am not going to pay $3 for a delivery fee, and then an additional $3 for a 20% tip on $15 worth of food (for two people). That would cost around $21 dollars...or a 40% tip.
If a business does that, I will limit my overall additional costs to around 25%. So, the $3 delivery fee + $1 tip = 27% additional cost.
Sadly, the driver will only get about $1-2 of that $4 tip. That's on the business, not me. I am not supplementing for these businesses taking a cut of the delivery driver's wages in tips. Then again, in the US, the owner is never to blame...and then incorrectly cite laissez faire.
Also, if food is spilled in the bags, and the driver doesn't mention it (i always check my food before I pay)...I won't tip. Might be different if the driver is upfront and apologizes...but in a college town, spilled food is pretty common especially when I order chinese (and they usually just hand the bag smiling regardless). But, if the driver is FAST, I will tip another $2-3 in addition to what I was originally going to tip.
If we are forced to play into this idea of tipping being an incentive (which it's really about forcing costs on customers rather than servers) then I will punish/reward through my tip and not feel bad about it. The funny thing is that in the US it's never the servers' fault and there is this idea that you should always tip, but then again, there is this ambivalent idea that there is some incentive in the tipping system...I call bull on this contradiction.
If there is a gratuity charge for a party of 5 or more (15-20%), I won't tip anything additional. Then again, why the hell should I have to tip a certain percentage? That, again, defeats the whole idea of there being this incentive system.