What the heck is a wheel alignment and why is it important for my car?

A Wheel alignment is the adjusting of the angles of your car's wheels relative to the ground to achieve maximum tire life. A properly aligned vehicle with good tires should drive straight along a level, straight road.
An alignment is recommended once a year for a couple of reasons:
1. There are various moving joints and rubber bushings in your vehicle's suspension system that wears very slowly over time. As these parts wear, the wheel's angles change and need to be re-adjusted to compensate. These parts should be routinely inspected and replaced if they are worn beyond a normal threshold.
2. Running through a good size pot hole or even hitting a curb can very well knock your car's alignment out of whack - ouch! I think we're all guilty of that!
It is also recommended to align your car when you install new tires; that way your new tires get a fresh start for the longest life possible! 
A Wheel alignment is often confused with wheel balancing. Both can affect the quality of your ride, but in different ways. If your wheels are out of balance, then you may feel a vibration at highway speeds through the steering wheel and/or the seat. If your alignment is out, it can cause premature tire wear, poor tracking and an off centered steering wheel.