I tried to connect to an XMPP server, and was rewarded by a certificate mismatch error. Telepathy doesn't provide any way for the CM to tell higher levels what exactly the mismatch was, but I thought "hey, I'll look at the debug output". The debug output told me: "SSL Certificate does not match name 'server.i.was.connecting.to'". Loudmouth's error message included the name on the certificate as well, which would have been useful.
wocky_tls_session_verify_peer() would need to grow a way to return extra miscellaneous information about the certificate it checked for this to be fixed.
(I tried to connect with Loudmouth but it fell down a well during starttls, so Wocky still came out ahead. :))