Recently my system was pretty unstable, and I even ended up reinstalling the OS (and posting about it in evan for some reason). But more prodding today revealed panics whenever a process iterated over the files on the RAID. Some reiserfscks showed there was corruption, and I was getting pretty nervous, until Matt pointed out there'd be no way for the OS to know if one of my disks went bad.
So I unplugged the oldest one (which, happily, was only part of the RAID-- the other disks that support the RAID hold other stuff as well) and rebooted, and now everything is solid again.
That old disk was the disk that held all of my data last year. Had I not set up that RAID, I just today would've lost pretty much all of the data I have. (It's 92gb so I don't back it up.) It was definitely worth all the effort to make it work.