How to distribute Partitions across multiple HD?

[Knapp]

> use the fast drive for system and the slow for data

But what does that mean really?
/ root where?
bin Where?
home where?
sbin?
lib32?
lib64?
etc

How much is each used and when?

I know this is a complex question but there must be people that have
solved this many times before and methods to do it best.

Is there a program that might track this sort of usage and allow
things to put in the right place? What is the optimum number of drives
for a home system? How would you find out? I would bet that two 100 gb
drives would be much faster than 1 but what of 3,4 or 10? How does
RAID fit into this speed issue?

Thanks all!

Douglas