Drives in RAID arrays are very good when it comes to sustained transfer of large sequential files. The raptor drives, while also good at continuous reading and writing also have a much better seek time than standard 7200rpm drives (in fact drives in RAID 0 often have a slightly worse seek time than a single drive but the RAID array has to wait for both drives to be in the position to read/write rather than just waiting for one).
What this mean in the real world is that when dealing with very large continuous files, such as movie files the array array will be slightly faster. When dealing with lots of small files the raptor will be faster, loading windows for example will be faster on the raptor but you will see no improvement on with the RAID array.
JammyDodger is right. For operating systems, the seek time is critical. For other files such as videos, music, and photos you will see improvements with a raid only if your other hardware (processor, ram, motherboard) is less than a few years old.
I have a 36GB raptor for my OS and programs, and then two 250GB Seagates for my dump drive in raid 0. I love the raid, and like the raptor.
Note: the 10k rpm drive is by far the loudest drive I've owned, and it speeds up your loading times but not by leaps and bounds. Windows only takes about 10-15 seconds to load compared to about 15-20 seconds with a decent 7k rpm drive for my computer.
It's a catch 22 with a Raptor IMHO. I bought the 36GB raptor to hold me over until the next big technological advance with hard drives which will be a welcome change because hard drives are so freaking slow.