Since getting ID, i've very rarely been asked to show it. That was even when i went to Scotland. In the whole time i was there, i was asked once. And that was in Weather-spoons on the last day.
It is their jobs at the end of the day, but it sometimes annoys me. Especially if you were served by the same person 1 day earlier and they ask you for ID the next time you are in. I did get away with it once, only because i asked for immigration papers to the person who asked me for ID. True story as well, let me have the beer because they couldn't present the papers.
I understand the night-club perspective of things, but even that annoys me. They only seem to ID the lads, never the girls (for obvious reasons). I once was out clubbing and saw 3 16 year old females go into a club without being ID'd. Reason why, they had a fair good size on the chest. Told the bouncers who told me to bugger off, so i found a cop and told him. They soon shifted into gear and got the whole club ID'd.
Other than that, i do take it as a compliment when i do get asked. Never leave without it either.