lloydmuc,
I guess it varies, i have seen drives that are toast still get detected in the bios but be unusable. They are older, so may new drives just stop getting detected after they are toast.
bigbender_mike, Thats a very hard task, data recovery companies do perform such tasks(In a clean room). If you have nothing to loose go for it, but remember even a spec of dust can scratch the crap out of those platters rendering data(some or all) useless.