Both Windows machines and Macs come with a toolbar that runs across the bottom of the screen. In Windows it's called the "taskbar" and Mac OSX calls it the "dock", but the idea is the same on both. It's a place to show you running applications and launch new applications. It's the core UI element in any desktop operating system.
Have you ever wondered why it runs along the bottom of the screen? Well I have. From a UI standpoint it makes way more sense to have that bar running along the left or right side of the screen instead of across the bottom. Windows and OSX both let you move the taskbar (just click and drag it in windows - I don't know how to use Macs so you're on your own there). I want to briefly explain why you should give the vertical taskbar a chance.
Vertical space is more important than horizontal space
This is by far the most important advantage to moving the taskbar to the side of the screen. Even though monitors keep getting wider and shorter for some reason, the vertical space on your desktop is much more important than the horizontal space. Think about the things you do on your computer. You look at websites which generally have a fixed width (which is smaller than the width of your screen) but websites almost always expand beyond the screen vertically. You have documents where each page fits the width of your screen but you have to scroll down to see the bottom of the page.
Unless you're a graphic designer, chances are that you need vertical space more than horizontal space. By moving the taskbar to the side of the screen, you open up valuable pixels at the bottom and you're only sacrificing the mostly worthless pixels on the side of your screen which are probably just showing blank white space most of the time anyway.
The side of the screen is easier to reach with your mouse on multiple monitors
If you use more than one monitor (and you really should), placing the taskbar on the side of one screen which borders the other screen makes the taskbar closer to the middle of your desktop. No matter which screen your mouse is on, you'll always be pretty close to the taskbar. This is a small but very real efficiency boost.
You may be thinking that it's less efficient to have the taskbar on the side if you only use one monitor. I don't think that's true. The bottom of the screen seems like a more natural place for your mouse to end up, but that's only because you've been trained that way. Spend a week with a vertical taskbar, and I promise you'll find that the side of the screen is just as accessible as the bottom.
Applications fit better on the taskbar
This advantage mostly applies to XP and Vista users, but it's worth considering even if you use Windows 7 or Mac OSX. Because text goes from left to right (rather than top to bottom), each item in your taskbar has a fixed height, but a variable width. It only takes a few open applications running along the bottom of your screen to fill up the whole screen. But when the taskbar is pinned to the side of the screen, you can fit dozens of items on it without it getting too cluttered.
So what do you think? I know that no one will actually change their ways because of this post, but I really think you should give it a shot. I bet you'll end up switching back to the normal taskbar layout, and I also bet you won't have a good reason for doing so. Technological inertia is a dangerous thing.
P.S. I really don't like the Windows 7 taskbar. For some reason Microsoft decided to copy one of the worst design decisions of OSX (when there were so many great OSX features they didn't copy).