Guiness is about the only beer I'd drink out of a can I think. The malty chocolatey notes just about cover the horrible tinny flavour, and the pour you get seems to be nicer than out of a bottle with the nitro widget thingy. Without the smooth creaminess I'm not sure what the point of drinking Guiness is, there are much nicer porters and stouts flavour-wise; it's the texture that does it, I think. So yeah, much better out of a tap.
But, in general, beers in cans are just bleuuughghghughuhguhgh. Unless you like the zingy flavour of aluminium. Mmmmmmmm, aluminium....