All you need to do with Mac is copy the drive to another partition and it will boot. Carbon Copy CLoner or Super Duper do this easily and you can schedule it, no need for an actual RAID 1 set-up. Obviously Windows is more complicated.
Such tools also exist for Windows, but the point of RAID 1 is in case of a critical hardware failure(whole drive bricks). $60-$80 for a second drive as a mirror is far cheaper than even a tape drive. The motherboards all have this capability as well now, so why NOT use it? RAID 0 for boot, though, is asking for trouble.
Again, not with Macs --- you can use the OS software to raid partitions. Lloyd and I tested RAM disks and they fell WAY short in the performance compared to even a simple 2-drive stripe (RAID-0) on a pair of off-the-shelf SATA 2 spinners, at least on Mac.
This is a myth, though, since it's the same INTEL boards running most Apple machines. Partitioning the drive doesn't deal with the bandwidth and i/o issues of having multiple partitions on the same drive or multiple drives on the same channel/chain. Now, Apple does better here than Windows. Windows is officially I/O brain-dead by comparison.
Note - by Ram disk, I generally meant a physical DDR based hard drive. Or a simple small SSD. For a swap or temp space you don't need a very large one, either. The typical solution then is to just drop a 4-16GB SSD in the machine and use it for that. Sometimes, though, using physical (system)RAM can help for little or no cost - better and cheaper than a new drive and running RAID. Versus nothing at all, even a 1GB ram disk like this is a god-send. Shoot, just moving the swap file to a second drive other than the OS drive is a good 50% speed boost.
I've experimented as well and nearly RAID 0 speeds are possible in Windows if you just drop the swap and temp directories to a SSD.(bit trickier with Apple here, which is why you didn't notice much difference - since Apple has it set up to not be easy to alter its default swap/directory assignments) Also the typical end of program disk-thrashing is GONE so you quit and your machine is instantly ready.(big issue with Windows, IMO) SSDs are amazing, really.
Not necessarily. I am running my OS on a pair of WD 640 Caviar Black drives in RAID-0, not the RE versions -- again using the OS RAID capability, no controller card and I get very fast boot, I/O and a huge, fast desktop for dropping stuff on. My image storage array is on a 4-drive RAID-0 of WD Caviar Blue drives -- two partitions with the fastest outer partition of each drive in it's own dedicated 4-drive R-0 array for scratch...
A 4 drive RAID 0 array X2 on the same 4 drives is a time bomb waiting to go off. Anything glitches and you're gone. Now, I can see RAID 0 for a large file repository/applications drive, but the OS should be as bulletproof as possible, IMO. Restoring files isn't a big deal. Restoring and installing a new OS is a nightmare for Windows(less so for Apple, you're right)