These replies are all incorrect.
The clearing process just needs 1 confirmation, but that confirmation sometimes can be a bit a longer wait depending on the amount being sent for the miner to find.
If the output is too low you will need more confirmations or pay a higher fee.
At least one confirmation. That's when it is definitely in your account.
1 confirmation and you can calmly breath. It usually takes 3 confirmations or more before you can send it to wherever you want it to send.
no wallet will spend non confirmed transactions.
You will need at least one, otherwise double spending would be too easy
The right answer is that the protocol allows spending of unconfirmed outputs, so it depends on the wallet (and the miners). A wallet might prevent (or just discourage) spending unconfirmed outputs because doing it can lead to problems for the user. Despite that, most (if not all) wallets require 1 confirmation with some exceptions.
Blockchain.info does not (as far as I can tell) allow you to spend an unconfirmed output, but other wallets do. On the other hand, blockchain.info's shared coin feature does spend unconfirmed outputs as part of the mixing process.
Bitcoin Core allows you to spend unconfirmed change outputs.
Miners decide what transactions they will include in a block. A miner can decide to exclude transactions that spend unconfirmed outputs, but that would be rare.
The confusion about the 3 confirmation wait is probably due to exchanges requiring 3 confirmations before you can do something with a deposit, but that has nothing to do with Bitcoin.
