Here's a web site which discusses partitioning approaches click here
Personally, I think its a bit OTT, but it does consider many aspects and is a good read.
Yes, when you next format the hard drive is an ideal time to setup extra partitions, although more than 2 or 3 for average home use is stretching things IMHO. But I do try and get my boys to install their Games on a separate partition, so that would push it to 3 / 4.
Hope that helps.