Once you have a proxy application in between, though, this whole security feature stops to work. Not only will you not be notified that the application getting the password in the end has changed, there could even be a completely different application asking for your passwords without you having a chance to notice that.

I am not saying that this is a practical problem today – most certainly it isn’t. But it’s mainly “security by obscurity” you are getting there. As useful as such a tool for accessing the keychain can be for private use, as dangerous it could be once it sees usage in public. I guess it all boils down to the question whether you are prepared to grant access to your passwords to an application which will just pass them on to anyone who bothers to ask.

It could be interesting to discuss what Apple could do to improve their keychain API in that respect. While I think the traditional ‘ask for each application’ approach is a good balance of security and not annoying the user too much, the very fact that OS X is a Unixy system that lets you tie applications together through little helper applications and scripting languages makes this approach a bit weak in some cases.