I've lived in the UK my whole life and the few American's I've met have unsurprisingly had easily discernable American accents (even those that thought they had none).
I met a lovely couple from Missouri who appeared to have a certain amount of Southern drawl in their tone and and intonation, they found it fascinating that this could be distinguished in their voices...
I agree with Ustwo's comment as well, about American's (generally) being really forthcoming with information about themselves/family/personal history etc... all within the first 5 minutes of conversation, which is a testament to their openess and general friendliness.
I've always found it funny that the 'baddie' in Disney cartoons carries an upper-class English accent, I guess this is because it is considered more 'reserved' and as Irateplatypus says 'intelligent'. Although I reckon that's a nice way of saying 'smug and superior', which is how I would have thought this type of accent would come across... Like in the Simpson's episode where Homer has a huge sugar pile and a posh, Englishman shows up drinking a cup of tea: "I nicked it. While you put your guard down for that splitsecond. And I'd do it again!"
Now as for me personally I don't consider myself to have an accent because I've never lived in a city or countyside long enough to pick up a city tinge such a chirpy cockney accent or a regional dialect such as a Dorset simpleton "I've eard umm zay" = "I've heard them say". But I feel sure that to anyone not from this rainy island I'd probably sound like someone from the Monty Python crew... Go figure!
She stole my accent!