Straight to the point: These are cheaper, almost as fast as SSDs, and they're server certified to my knowledge (24/7 operation and good reliability). I will be using an SSD for my boot drive, a Velociraptor would just be for everything else, eg. Steam games, most applications and mass storage.
But, are they loud? And are they reliable enough to use in RAID 0?
All answers are much appreciated :)
Heat and power consumption is what you need to consider. And if you think about it, the capacity isn't that top notch partially in today's demands.
But other than those, I think they are good drives. The vibration has been cut back down alot over those old Raptors (in idle), so it's not as loud as those hard drives from the 80s. But do remember that in RAID 0, you risk of losing everything on that array. Alternatively, if you want to stripe the drives, gain more storage space AND have redundency, then RAID 5 is the way to go, as it uses parity for calculation. The only thing about RAID 5 is that you'll need a minimum of 3 drives, cause 1 drive has to act as a fault tolerance drive, while the other 2 are used. Find out more here (though since you said you know about servers, maybe you'll get the idea).
I currently have two 300GB Models in RAID 0. They are fast, but no where near a good SSD like Samsung's 840. They are very quiet (though I cannot tell for sure as the fans on my AMD cards are super loud) and run like champs. I've had then for 3 years now, though i'm looking to get some SSD's now.