Many years ago I did use a data recovery service for a business problem - unfortunately we had exactly the same experience as Bob's Vet did!! Yes they got much of the data back, but it was in such a mess that it was virtually unusable.
Needless to say that both business wise and personally I am now very anal re backups!!!!!!!!
Nigel
 

I think that freezer thing might cause metal within to contract, possibly moving heads that were out of alignment - I think at best that it would be a crap shoot.
 
I much prefer taking the backups I currently do, secure in reasonable protection for my data.
 
Most folks that have experienced a profound data loss don't let it happen a 2nd time, by moving to some sort of backup plan.
 
Bob Bone
 

HDDs are all similar in that the media is an optical flat (incredibly smooth), so if the heads come to rest on them they can actually stick (called stiction). The media is coated with an oil, so it can cause this to be even worse. Heads actually "fly" 1-2 micro-inches from the surface of the media and in the days of old, the parking area was on the inner region which was purposefully pitted with a laser to make it not smooth (reduce stiction). Nowadays the arms are actually parked up a physical ramp which is driven by a capacitor in the event of a power failure to keep the heads from ever touching the media.
 
Depending on the year/model, the failure cause by stiction can actually rip the head off the arm (worst failure there is), since the head cannot achieve flight without the disk spinning, but there are several other less destructive modes of failure. If the media is not scratched from a failure, the data can be recovered, but the drive cannot be powered on if not reading (since it can potentially scratch more). With newer heads (MR technology), a head bumping the disk can cause a thermal spike (thermal asperity) which can cause it not to read properly for a few seconds... or actually rip/damage the write head itself. From a read perspective, neither with promote "disk failure" and the head may still be capable of reading.
 
Most drives will show degradation rather than catastrophic failure, so clicking (from excessive seeking) is a good indicator to 1) leave the drive spinning to prevent a catastrophic failure and 2) backup the drive immediately (even if simply copying it).

I once made use of a data recovery service and they were able to successfully recover the data.

The problem is that if the file table can't be recovered you'll end up with a seemingly endless list of files that you'll have to go through to get the data you need. Fortunately they were able to tag the files that were part of the Operating system so that took care of about 1 million files I didn't need to go through but it was a lot of work.

In the end I decided to look for files of a specific type and be done with saving just those.

Since then I've always saved created data on separate drives so that I can easily ask it up.

Thanks, everyone, I didn't realize this thread had more responses!
 
The drive is (or was) a 1TB 7200RPM Seagate SATA III drive used in an external enclosure.   It began with a consistent clicking sound that I happened to notice when walking into the studio one morning.   After unsuccessfully getting it up and running I turned it off.   I later tried again in a different enclosure but after a few seconds of clicking it went silent...   That's about where I stopped.
 
I fortunately had a second matching drive (also bought in 2011) that I never wound up using so I've since collected all my sample data back on that one.  I've also backed up everything copied over as I've went along, to a second internal drive and an external 1TB WD drive.   I plan to get a 2-3TB drive to act strictly as a backup, otherwise turned off and disconnected to preserve its lifespan.
 
FWIW, the cheapest clean-room service I found was $500, and there was no guarantee.  Everything else was in the $800 and up range.   Needless to say, I couldn't justify the cost, and based on some of the comments above regarding the lack of a TOC, sample libraries could be way more of a mess than not.  
 
Anyhow, thanks again for all the responses, I most definitely appreciate it.    Good discussion!

The click of death is usually definitive.
 
"Easy" data recovery can work if the disk is seen as a disk, but the file system is poop.
 
Clicking means the head motor is not happening.
 
For way important stuff, the disk is moved to another same, or a way expensive drive.
 
A friend was able to move a disk for me. I was lucky to find a 2nd drive with the exact same model numbers.