@ Octavious: "All a UK barman actually does is pull a lever or open a bottle, which is a skill so easy it can be learned in minutes and hardly worthy of a tip"
That's harsh. They also have to change barrels in the cellar, clear up empty glasses, act as a host and converse politely with patrons. They generally have to help manage stocks, and sometimes often have to act as security staff as well, dealing with any troublesome or overly-intoxicated patrons.
A *good* barperson should know something about spirits, too, especially if the bar has a decent range of, for example, whiskies. And if it's a real ale pub, you'd expect the barman to know something about the ales they are serving.
In many UK pubs that serve food, the bar staff also have to act as waiting staff (and yes, they *might* get tipped for providing food service).
@ Abgemacht: Do you guys not have mixed drinks across the pond?
If you mean a gin and tonic, or a Jack Daniel's and coke, sure. But most normal UK "pubs" don't offer a cocktail menu, and generally you shouldn't expect cocktails in a regular pub - there are special high-end wine bars and cocktail bars which offer this, but regular pubs often don't.