Beer is best served ~3 degrees (~37.4F), at ~1 degree it doesn't aroma properly (most taste comes from smell) so a flavourful beer like Guinness will taste life

Beer is best served ~3 degrees (~37.4F), at ~1 degree it doesn't aroma properly (most taste comes from smell) so a flavourful beer like Guinness will taste lifeless, however over ~5 degrees a beer can become warm rapidly and unappetising. In the UK casks are supposed to keep below 13 degrees (~55F), however this isn't always the case. The places I frequented had a refrigerated cellar and IIRC kept it around 9 degrees. The reason why beer is served so comparatively warm in the UK is because of an age old tradition for the workmen coming into the pub; essentially you order two pints, the first one should be finished before they've finished pumping the second, and the second shouldn't last too much longer! Dark beers like Guinness do, however, stay cooler longer than the light lagers, so perhaps this is another reason to the reluctant change of chilled beer in the UK, but I'm certainly not against it.