It has been shown that partitioning can help read/seek times greatly, but personally, i have not seen much, if any, increase.
I have four HDD's split into 12 partitions. one for games, one for game backups, one for OS, three for music, and six for random data.
The one thing that is nice though, is defragging. Defragging a 50GB partition is a lot quicker, and nicer for me because i defrag often, than a 200GB partition.
Manual file sorting is a little easier, IMO, with more partitions.