I'm getting quite a collection of full/old hard drives that have been replaced with fresh ones over the years. I keep them all as a backup to the backup. They sit there, labeled and tidy in their static-free bags, waiting for that weird emergency that would require me to access them.
Of course, the nasty part about all those drives is that they aren't in any kind of enclosure. So if I DID want to access the contents, I'd have to open my MacPro and put one in a drive sled. At least until last week.
I bought a USB Drivedock from Weibetech and it's the perfect solution. For about $50 U.S., it will read:
2.5" (notebook) SATA
2.5" (notebook) IDE/PATA
Simply plug the thing into a power source, connect the appropriate cable to the drive, and connect to computer via USB. Power on and the drive mounts. Very cool. Especially during those times when you're swapping/replacing drives but want to maintain something from a drive you're removing.
For instance, I just ordered an SSD for my system and applications drive and was able to remove a couple older drives knowing that I could access the stuff whenever I wanted.
Just thought I'd mention it if you have a collection of old spinners laying around.