Its probably been posted before, but a day spent bumbling around YouTube has found this little gem:
Its a bunch of (right handed) guitar players trying to play a left handed guitar, either upside down (so the strings are the wrong way round) or totally left handed - ie the hands are doing the alternate actions. I've just tried it and got nowhere (by turning my right handed guitar upside down) and it makes you completely think again; and appreciate what its like for a complete beginner etc.
Personally I am left handed myself but when I started ages ago, never tried it lefthanded and just picked up and learned a right handed guitar etc.
PS I got to 21 mins of the video before I had to click it off, due to the noise.