Not that I care one way or another about Zuck getting a reputation for being cheap, but when my own wife and I were planning out honeymoon to Florence and Rome we inquired about tipping habits overseas and were told it wasn't usual there and it really came about due to American tourists habitually tipping. We were told if we we're really happy with the service to leave a Euro or two at the most, which is what we usually did.
Tip in the wrong context and you risk offending the service provider. I've been told never to tip a British pub keep, offer to buy him/her a drink instead. Not sure if times have changed though.