Er! Think it does affect a lot more than you may think!
Having worked in more than a few pubs in my time, I think this problem will affect more than 1 or 2 Register readers.
In fact, any one who has Ice in their drinks, or has beer from a pump or tap.
I've found a fungus in many ice makers, check to see if there are black spots in your ice - and No, I am not joking.
Also, the pipes delivering your beer from the barrel or keg should be cleaned each week using a recommended chemicals, plus there should be, as in the best bars, a wash with clean water after every barrel change.
The yeast from the beer can mutate into interesting variations if left un-attended, and can lead to victims calling on the Great God Huey on the Cosmic Telephone.
A pub with a regular cleaning regime is a good pub - they will probably look after the beer better as well. Ask the bar person when was the last time the pipes were cleaned - if they don't know, drink elsewhere.
Personally speaking, I prefer my beer to pass through my kidneys and not pass my tonsils on a return journey.