Related to Issue #1637 :
There should be an ability to mark some private keys as frozen so they won't be used for anything. It would be additionally useful to have a key both frozen and neutered, so that it's effectively watch only and the data isn't even in the wallet.
This can be used to avoid contamination from commingled inputs, to set aside special inputs that are to be used in contracts, or to create watching only wallets for improved security.
For a more concrete use-case, I'd like to use this feature because the #bitcoin-otc WOT supports bitcoin address authentication now. I created an address for signatures, but would prefer not to use it as inputs by default, because that would allow people to correlate my WOT identity with actual transactions on the network, which is undesirable. For example, someone sent me 0.92 bitcoins as a prank to my authentication address, which was annoying because I have no way to prevent them (in the mainstream bitcoin client) from being mixed up with my main wallet. Luckily, I was able to send all my coins off to a different wallet before the 0.92 transaction confirmed, and then sent the 0.92 elsewhere, but it was annoying, and could be done at any time.
Agreed.
Though watching-only wallets don't need the private-key at all, so I think that's a distinct feature.
