I have always thought that there really needs to be some trusted third-party verification service for Bitcoin addresses, which would work in a similar fashion to an SSL CA. I don't believe the pgp-style web-of-trust model gives enough guarantees (or has enough defense against bad actors (edit, CACert is pretty close)) and using a cryptographic solution invites namespace-collision problems (i.e. the super secure third-party escrow solution at casacius.com.)