0 is roughly the temperature on the coldest series of days in most of the continental United States and Europe, and 100 is roughly the hottest.
Celsius is great for measuring water while cooking. 0 is freezing (at sea level, assuming a normal room temperature) and 100 is boiling (again, with caveats).
The metric system has everything evolving around a cubic meter of water, so Celsius is easy to grok, and feels logical.
But, having lived in the U.S. and Europe roughly an equal amount of time, Fahrenheit is much much more accurate to estimate outdoor temperature with.
And as it turns out, that's what most people are doing.
Cute asides: The meter is based on a miscalculation of the distance between the equator and North pole. The SI couldn't find anything absolute that actually matched their arbitrary size, so made it dependant on a bar in the SI building, and then realized the bar is changing sizes with time! (This is finally being rectified with some atomic measure.)
On the other hand, my sixth grade teacher taught us that 0 is the freezing point of beer, and 100 is the body temperature of a cow. So, the theory is that some drunk scientists thought a cow had fever..