Stealth's link pretty much covers it... but here is my experience:
1) If you get the raptor, you won't have any issues which come with RAID
2) The Raptor will be hotter than one drive, but the two WD's might be a bit hotter (not by much though as the WD's run very cool)
3) I would go with the WD RAID 0 array. I have a 2x250gb Seagate Raid 0 array and a 2x160gb WD RAID 0 array. Both Arrays are really fast.
My father's PC (I build my sons, brothers, and parents machines) has a 74gb Raptor in it, and it is nice for a single drive, but it is not a RAID 0 array.
The 2x160gb RAID 0 will boot faster, have faster read times, and greater size than the raptor. The random seek times will be slower (they will be the same as a single 160gb 7200rpm drive) so when accessing a bunch of small files (really small, for instance if you were copying a couple hundred word documents that were on different parts of the drive you might notice this), but files as large as MP3's will fare better on the RAID array.
You do get to tell people you have a raptor in your machine, which is something to be considered. The difference is the same as between drinking Maker's Mark or just regular liquor. If you care at all about a "blue sky" name (Rolls vs. Ford) the raptor is the name, but RAID 0 has more "nerd cool points" attached to it.
I personally reccomend the RAID Array... just make sure you monitor the SMART data closely, as recovering data from a dead striped drive is hard.
If a drive does start to die... buy a new one of the same specs (cache, speed, size...) and use a utility like Acronis to clone the drive bit-for-bit to the new one. problem solved.