I've had a few drive failures, and each time, I copy important data off the drive with the array in the degraded "emulating missing drive" state and create a list of everything else (windows shortcuts).
Only then do I rebuild the drive using a new hard disc. That way, if there's another drive failure during the rebuild, it's not the end of the world.
I also run a cron script overnight that records what data is on the cache drive in case that dies:
0 4 * * * ls /mnt/cache/TV >/mnt/disk1/Backups/TV-cache.rtf
0 4 * * * ls /mnt/cache/Movies >/mnt/disk1/Backups/Movies-cache.rtf