Cleaning the chain and cassette every 100 miles seems excessive, unless you are riding on a lot of dirt/gravel roads and/or in the rain.

Here is a nice chart to schedule maintenance. Scroll down a bit to see the chart. I have it taped up inside my storage closet door where the bike cleaning supplies are kept.

http://bicyclehabitat.com/how-to/a-s...hart-pg366.htm

I lube the chain every 100 miles or so, or when it gets noisy or shifting seems sticky. But I only clean everything every 1000 miles or so. Or when it's really dirty. Or not.

I rarely ride on anything less than an unpaved road, and almost never in the rain. Rain changes everything, and while I don't really mind riding in the rain, I really hate cleaning up the mess afterward.