I ended up going to the local pub and indulged in being Oirish (cue terrible accent) and fell into Guinness's marketing ploy whereby for every pint you bought you got a token and once you'd collected 5 tokens you got a silly hat and a few badges.
I never drink guinness but I'm glad I did last night - look at all the free stuff (not really free when it's £2.70 a pint!) I got!
P.S I've always heard the rumours and I can confirm that Guinness does make you poo very dark! No photo evidence for this though, sorry, maybe next year.