In the UK, I never tip hairdressers, and I believe that tips in restaurants should be in line with service recieved....poor service = negligible tip, excellent service = ~10%. I find it galling in the US where you are expected to tip up to 20% even if the service is very sub-par. And tipping a bartender to pass you a drink across the bar?

Taxis....I don't tip in percentages, but round up to the nearest pound + £1. I'm more inclined to tip minicab drivers as for a comparable distance, the fare is much more reasonable than black cabs.