I'm a lefty. I originally started with a right handed guitar, and found it very slow to get anywhere. I got a left handed guitar after a while, and it felt much more comfortable, and I learnt a lot quicker. I do almost everything left handed, except using a mouse, and I think I use a knife and fork the right handed way. My brother writes left handed, but does a lot of stuff (including playing guitar/bass) right handed. Unfortunately I don't seem to have got the creative aspect of being left handed, despite how dominant my left hand is. I can play a right handed bass upside down pretty well though (well, not a lot worse than I can play a left handed bass, which isn't much above average). It's a bit of a 'party trick'.