I learned the etiquette of good tipping when I became a waitress, during My college years.
Unless the wait person is a daft ********/prick, 15-20% is appropriate if you have excellent service. Just today I had a great, *cheap* Cuban meal where the counterperson was extremely sweet and helpful, where the bill was only $6.50--I left $2 for tip.
Yes, Europeans have no concept of tipping, which I think is a horrid attitude. I am slowly teaching My English boyfriend about the value and importance of tipping.
As far as NYC cab drivers go, I always tip $1 and loose change whilst in Manhattan, and a whole $2 when going to another borough. If I have the good grace to have a funny, gregarious cabbie (My faves are Haitians and Jamaicans!), I'll tip more. A trip to or from the airports merits $5.