Tom writes
"Of course, the accent of most Britons is quite different from RP, so you will probably stand out anyway. (Speakers of GenAm will have a much better chance of blending in with Americans, as there are fewer regional differences in the US.)"
http://www.antimoon.com/how/pronunc-american-british.htm
This is assuming that you manage to perfect RP/GenAm. Most students can reasonably expect to stand out for quite some time. Also if you can manage RP, you'll probably be able adapt your speach.
What he's trying to say, I'd speculate, is that a person speaking heavily accented GenAm will find an easier time blending in than someone trying to speak accented RP.
A foreigner speaking fairly fluent, but accented American English is by no means a rarity on campuses and in larger cities. If he shares some common interests with Americans (be it science fiction or jam making or wife swapping) and is reasonably likeable, he'd be sure to find American friends.
A foreigner speaking fairly fluent, but accented RP is a stranger everywhere. Working class Brits dislike RP, Americans find it classy but distant and somewhat cold.
An international career man studying English purely for business and professional reasons would benefit from speaking RP.
On the other hand, anyone who wants to spend any amount of time in an anglophone country or have anglophone friends, should avoid Received Pronunciation.
I had a long conversation with a Swedish woman in English. I am a native speaker and we had this conversation in Poland. I could not fault her pronunciation but after a while I steered the conversation to old television programmes. At a certain point she said that she was Swedish and speaking English as a foreign language.
British people are very aware of slight differences in accent and word choice etc. On the other hand, that does not mean that British people do not accept people who are not British, who speak English.
London in particular is a melting pot of different nationalities.
One in nine British residents was born overseas - Telegraph
25 Feb 2009 ... One in nine people living in Britain was born overseas, according to figures that highlight significant changes in the population under ...
www.telegraph.co.uk/.../One-in-nine-British-residents-was-born-overseas.html - Similar