Its personal preference. I dont like to partition anything smaller than 120GB cause you might run into space issues later on with the OS partition. If you partition it into say 40GB and 40GB I dont really see the point? Usually I would agree though to partion out a hard drive
the reason I say that is cause if you ever need to format and re-install windwos... you only have to backup the files you want from the OS-partition... the data on the other patitions will be perfectly safe.
I guess it depends on what you do. I had my OS partition at 40 GIG and ran out of space. I always forget to install my big ass games onto another partition..a few of those and that 40 is gone!lol. I then had my two other partitions one 300GB and one more 300GB. I have 615GB between all three full already..I need one of those new 500GB drives