I just read in an old copy of "Invention & Technology" magazine (Winter 2009) about Henry Ford's Model T car turning 100 years old.
The article produced the following claim:
"Ford relocated the steering wheel from the right to the left side on the Model T, a custom followed by other car makers, in part, so that women might more easily access the curb from the car..."
Of course, this is under the assumption that the women would be passengers, and would therefore keep them safer (out of traffic) and cleaner (out of the muddy street) by allowing them to get into and out of the car on the curb.
Who could have ever thought women would be ever be driving cars? :)
Also, though, a 1909 Ford brochure explained that putting the driver on the left would help see oncoming traffic clearer (since they would be closer), and help them judge distances when passing or making left-turns. So it wasn't all about the ladies.
Why we drive on the right in the first place is another question I'll get to when I learn it! But I thought you might like to know some of the justification for why you hop in the left side of your car everyday to drive.