Yet another advocate of the 10,000RPM drives here, you really need to use one personally before you can comment on them. One thing that everyone seems to confuse is that you buy a faster rotating hard drive for speed purposes, that's what you are paying for. You do not buy a Raptor for mass storage purposes.
In other words, you put your operating system and any other programs that you load on a frequent basis on the drive. They will load significantly faster than any 7,200RPM drive. A windows install for me takes about 15-20 minutes to get through the whole thing.
So get a Raptor for a primary drive, but only if you have the money to buy a larger 7,200RPM drive for throwing on your music, movies, pictures, whatever...
Why go 10k when there are 15k drives?
Because 15K drives are SCSI as far as I am aware. They are a pain in the *** to set up and run fairly hot. Support for them is limited, I can't think of any board off the top of my head that has support for SCSI.