[mjhall]

To add to grecy's comment:

Your login Keychain is usually unlocked - it's encrypted with a key derived from your password that's held in memory from when you log in.

You can lock your login Keychain (or any other) from Keychain Acccess (/Applications/Utilities) or from the security menu bar item (if you have it added) and you'll be asked for the password rather than asked to "allow" it.

[wamatt]

Ahh ok, subtle distinction. Thanks for clearing that up. :)