Bitcoin address book

I want to implement something like a "Bitcoin address book". I want to ask you guys if you find this a good idea or not.

The PROBLEM: when I send Bitcoin to someone I hope that the address I've copy-pasted (only Chuck types them manually) is correct, but I can't be sure until the money really arrives to the recipient.
Proposed SOLUTION: build something like a "Bitcoin address book". Users could go there (website), and assign a label to a Bitcoin address (they must first prove that this address belongs to them - using signing functionality of the Bitcoin Qt client for ex.).

This web application would have a very simple API which you can use to query the label of a bitcoin address.
This API could be embedded in the Bitcoin client or on the Cryptsy exchange website, so whenever you introduce an address you would get the label displayed next to it (if one exists). To make things even more simple, the Bitcoin client could be extended so it makes the label of the "receiving address" public (if you choose), and this label would be registered on this website automatically.

This way it would be very unlikely that you send your Bitcoins to the wrong place.
Do you think that it would make sense to implement a system like this? As long as people don't specify their real names as the address label it should be a threat to anonymity...