OEMS use it as a recovery partition.
ITs faster if you partition it.
Considering a standard mainstream hard drive of today 80GB/120GB, should they be partitioned or not? If yes, why? If not, again why? For a general usage PC what should be the number of partitions for both?
One more thing. Why don't OEMs usually use have partitions on their PC's hard drives?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic