IMHO (from the east side of the pond) all dark beers should be drunk at cellar temp, not least because, like erichbaumer says, there is an analogy with red wine in that coldness hides their complex flavours.
I no longer drink Guinness in pubs unless I am visiting Ireland. Firstly because in the UK it is always served cold and even (can you believe?) EXTRA cold! Secondly I'm not sure that the stuff brewed on licence outside Ireland is the same as that in Dublin; it certainly doesn't taste the same to me.
Many moons ago I played rugby for "London Irish". They told me I must drink Guinness. I replied that I didn't like the bitter metallic aftertaste. They informed me that the club imported its Guinness directly from Dublin and made me drink it! It was just warmer than cellar temp - a beautiful mellow pint with no harsh aftertaste - After six pints I admitted I was wholly wrong, but only about their sourced Guinness.