[adamt]

In most of Europe a tip is far more discretionary and often smaller. Eg In the uk I would not tip at all if the service was poor/average and perhaps 10% for good service. I would think of it as being much more performance related and far more discretionary in Europe.

I wouldn't feel bad about not leaving a tip and whilst a waiter/waitress might be disappointed they be overly wouldn't insulted.

In the US I've seen much wider range of people expecting a tip. Eg in the uk you might sometimes round up a taxi fair, but I've had a new York cab driver get positively aggressive (initially refusing to give us our bags) when we didn't tip after he his inability to find a major hotel had added $30 extra on the meter.