I have a few on my old desktop in my parents garage from the CPU mining days. If bitcoins REALLY take off, I'm gonna have to recover them.
If it does take off, and your drive didn't store well, you'll be facepalming. :P
I feel like I should go on my old laptop and dig up my ~0.5 bitcoins.
I wonder just how many bitcoins have been permanently lost already.
Early in the blockchain there are thousands of addresses with a single 50BTC block reward in them. Presumably people downloaded the client, mined a block and got bored. At that time you could only mine using Bitcoin-QT, which reuses the same addresses for each block reward. Most, if not all coins mined in this way are lost forever.
If it goes high enough, it will be worth mining trashed HDs for lost wallets.
Ug, somewhere I have a failed SSD with 10 of them on it.