Several years ago I moved to California for a while. When I arrived, I was amazed at the number of tip jars everywhere. When I was having some rennovations done by a small company, I asked the owner (a native of the area) if it was expected for me to tip her workers. Her response (and I paraphrase) was "No. I pay them for the work they're doing. The only people who should get tips are restaurant waiters and your hairdresser."

I think she hit the nail on the head.

Also, if you buy a Starbucks, Jamba, or similar card, there's no way to leave a tip on the card and there's no cash in your hand to drop into the waiting tip jar. Dilemma avoided.