I would have to say that the most prominant difference between British English and American English is Spelling and Pronunication

For example:

Honour and Honor

Colour and Color

etc

(In both cases, the first example is the British spelling and the second is the American spelling)

Neither is wrong and neither is better than the other.

Although as I have been told, Americans are easier to understand than British.

I do have to agree that accents play a major part in your ability to listen to and understand the conversation. Even I have difficulty understanding some British Accents, espically Cockney (London) and Brummy (Birmingham).

My partners english is excellent, sometimes I forget it isn't his native language, but he has trouble understanding me in some cases, espically if I talk fast.

:P