Cranky old bunch from my experience, which granted is fairly limited. Only times I would have bumped into them would probably have been the double-header QF's in 2006, when we played their Minors in 2010 and when they are neutrals at All Ireland Finals, but they always seemed to be moaning about something.
In particular a group of them were whinging in the pub after the 2009 AI Final about wasting their time and money coming down to watch another Cork team bottling it in an All Ireland Final. Lovely stuff to listen to when the head was already in a bad place and them with their one All Ireland in 125 years.
Just on my own experience Tyrone GAA folk seem to be a bit more personable, same for Down and Derry.