The way I see it is that a slow hard drive can be a huge bottleneck, since all the information you ever use with your superfast CPU and graphics card originally comes from the hard drive, right? So why not get one of the fastest drives possible? I went from a 5,400-rpm Seagate to my Raptor and it makes quite a difference - most notably, boot time and the loading time for Half-Life 2.
I've got a 74-gig Raptor for Windows, games, and apps and an 80gb external drive for music, storage, and things I want to back up. Works for me!
The Raptor does have quite a noticeable seek noise (it reminds me of computers that struggled with Chessmaster 3000), but I've grown fond of it. Think of it like revving the engine with a modified exhaust on a car.
The idle is quieter than my old Seagate.
Lastly, I don't think the 36-gb one is worth the money. I read somewhere that the 74-gig is slightly faster, and (of course) has 200% the storage capacity for a 50% greater price.