OSX asks for my user password pretty often -- seemingly whenever it needs to use Keychain. How do I make it stop asking me?
As you phrased this, it generally occurs because the login password was reset at some point, and now the "login" keychain is protected with a different password than the account as a whole. The other possibility is that the keychain is set to lock automatically. Both issues can be addressed using Keychain Access, which lives in your Utilities folder.
If you do not know the password:
If you do know the password, but Keychain is auto-locked