I tried that once, failed miserably. I have old backups so we'll see but most of the newer game saves are gone.
In regards to formatting. The old PS3 formats as soon as you turn it on after inserting a HDD even if you remove and immediately re-plug the same one.
However this is not the case with the Super Slim. If it detects the PS3 software in it and it's from the same unit, it boots up as if you never removed it.