Been using 750gig Caviar Blacks since I put together my last system. No problems whatsoever and the speed is worth it. But if I did more research, probably would have spent more for the 1TB. Reason is that they use denser platters, which gives a slight performance increase .. 1ms? Well, they were sold out anyways.
But if already have a system full of green drives, I still think the Raptor is a viable option for a substantial speed increase. If using it just for the OS and some apps, you really don't need it that big. Because if happen to get a much larger one, probably will end up filling it with junk, defeating the purpose of having a clean efficient OS drive.
Unless SSDs changed the last few months, I'd wait on them. Their performance is of the future, but I wonder if it's worth the extra maintenance. Firmware upgrades requiring another bootable OS to install, plus need to back up the data each time. Performance drops as it gets filled....but just deleting doesn't work so well. And many reports of people not getting the full potential out of them, unless with constant tweaking and maintenance...and some just can't seem to get it to work optimally. They are the best if want the cutting edge.
But with a Raptor you just connect and forget. And as an OS drive, might have to do a defrag once in a blue moon.