I was very disappointed when I found out they don't use TLS when federating XMPP. Basically, if you're chatting with someone who uses them for XMPP (Jabber) service, your stuff is riding in the clear between the two servers.
Edit: that came out a little curt. The OTR protocol is different than what Gmail calls OTR. Gmail's just turns off logging; the protocol is encryption.
It's been like this for years.