Even tho I was bustin' on FP for his number of partitions, I agree totally with him regarding not just using just one partition. I build and sell systems to people who are obviously not as big of enthusiasts as we are and I browbeat them into using the second partitions I create for them for saving their music, critical files, etc.
It saves me alot time as well since I can put all the drivers and secutiry software back there so when they come back to me with the C: \ partitioned all trashed, everything's there for me in case of a need for a fresh install.
I'm surprised ANYBODY in here would use just one partition especially if that's your only HDD!

I run 3 partitions across a RAID 1.5 setup and there are no stability issues. Not mention it being OCed + 500 MHz as well.
FYI on RAID 1.5.......
write = same speed as a single drive
read= about the same as a RAID 0, maybe not quite as fast.
redundancy= same as RAID 1*
*
If one HDD dies you can rebuild the array ( unlike RAID 0) with no loss of data using a like HDD as long as you use the same controller. In this case, the o/b Hpt372N on my DFI Lan Party revision A+. This is the only mobo I've seen with this capability.
It's pretty sweet.

AMD Ph II X4 955 BE 3.2 @ 3.8 GHz | Scythe SCSMZ-2000 | ASRock 880GMH/USB3 | 8 GB G.Skill DDR3 1600 | Radeon HD5670 | Kingston 128GB SSD