I recently RMA'd my ASUS P4C800 Deluxe and received a P4C800-E Deluxe, which supposedly has better RAID performance. With the P4C800, I only experienced a problem with the RAID twice over a period of a year and each time it was rebuilt with no problem.
I am using the same two Maxtor 160GB IDE 8MB ATA/133 drives in a RAID 1 (mirror) configuration, the same setup as before. Before defining the array I formatted each drive. I created one 30GB partition and one 125GB. Then I did a fresh install of Windows XP, got all the updates, and installed most of my applications. During that time I rebooted many times and the RAID was said to be functional.
Later on, I copied 110GB of data from a backup hard drive to the 125GB partition. I rebooted soon after and it came up saying the array was "critical." I rebuilt the array and everything seemed fine. I installed some more applications and rebooted a few times and each time the array was said to be functional.
I was about to call it a night and decided to defrag C: (30GB partition.) I did an offline defrag with Perfect Disk. After the reboot, the array was functional. I then did a smart defrag. On the next reboot the array was "critical." I tried rebuilding it again but it came up saying something like "cannot find second disk, or it has less free space than the source disk."