No. In a rare occasion where I have lots of bags, especially if I also have infants, car seats, strollers, etc., and they're really helpful. Usually I keep my bags myself and do not tip.
I tip the people who work at my local, independent coffee places, who not only make way better espresso and foam than anyone at any Starbucks in the world, but also chat with me and my wife, know what we drink, etc. I never tip at Starbucks when out on the road.
I actually do tip all bartenders, not sure why, it suddenly seems like it belongs in the "what stupid things have you done" thread.
Always some, like a waiter/waitress, my understanding is it's an essential part of their compensation. How much depends on the driving and the atmosphere in the taxi.

It's probably right to tip them when they successfully evacuate you from a burning airplane. You can also give them GTEM's, if you're not into the bribe, errrrr, gift culture.

One thing I never used to do, but always do now, is tip maids. That's a nasty job and those people make squat, and I think it's good for the economy for them to have a few more dollars that frankly my company or I really won't miss. Our travel policy explicitly allows tipping maids up to some reasonable level, and I support that completely.