Stephen Hackett talked a month back about where he kept his Dock in OS X:
I also just like the way it looks on the right side. I feel like having it on the left (with Desktop icons on the right) makes everything feel far away from everything else. The Bottom Dock is a waste of precious vertical space, no matter how handsome the new Mountain Lion version is.
This is a pretty nerdy topic, and I can’t help but chime in. I am a keyboard guy. I like to use the keyboard to navigate as much as possible. As a result I mostly use CMD+Tab to switch between applications. Then I use Alfred to launch new applications. So not only is my dock on the left, but it’s hidden, and only shows up when I move my mouse cursor to the edge of the screen.
The dock is great for more novice users though. It’s pretty, and easy to use. It blends the quick launch bar and task bar from Windows into one place, which means in theory it could take up less space. I love that you can add a bunch of folders to the right side (or bottom) and I really like having the Downloads folder there. In fact, the Downloads folder is about the only thing in the Dock I use regularly.
At the end of the day, this is just a matter of preference.