I accidentally hijacked someone else's hotmail account (and subsequently their abandoned Myspace account) because I was able to register the hotmail they used for it and then use forgot password to send a reset email on Myspace. I assume the same thing could be done for other services.

Well, my last experience trying to recover an old hotmail account was a few years back, so they certainly may have changed their policy since then. I'm surprised I didn't hear about the policy change though, I would have happily used hotmail for a good short name :)

I can confirm this is still the case. Story made me check old hotmail account - said the account did not exist and allowed me to create new account with same address.