I've been pretty amused with this thread... I think it boils down to this:

No tipping in many countries in Europe because service is included =

Positives:
Price you pay is price in the menu/card
No worries about offending anyone
Negatives:
If the service is crap, you don't have a say in it other than mentioning it to manager (which probably will not result in a discount on service)

Tipping in N.America =

Positives:
Staff earns their service money by actually performing.
You can withhold or lower the tip (generally) if service is pathetic
Negatives:
Always have to pay more than the price on the menu/card.
Never sure if it's too much, too little or just right.

And then you have the Southeast of the US... That's a whole different thing... :

Some bartenders give crap service and expect BIG (40%+) from people... Will treat friends (and occasionally the regulars) much better than 'tourists'...

Some waitresses will try to add the tip to the tab (very nasty trick, and we've had people FIRED because of that).

HTSC