The first and most obvious problem is created by right-handed desks, forcing us lefties to reach across our bodies to write with no support for our arm. Now, granted, there are usually one or two desks in a classroom for left-handers, but with 8-10% of the population being lefties, that leaves a shortage of left-handed desks in every classroom in America.
The fact that the English language is written from left to right creates an even bigger disadvantage for left-handers though, because it forces us to push the pen across the page. This is in stark contrast to all those righties who get to effortlessly drag the pen across the page while resting their arm on that comfortable right-hander desk of yours.
Fortunately for us lefties though, we're inherently smarter than our right handed counterparts:
http://isittrue.msn.com/slideshow.aspx?cp-documentid=1319838...
Who's to argue with Einstein, Newton, Franklin and Picasso? :)