A key feature in RabbitMQ 1.7, unmentioned in this post, is native SSL support. Before this version, stunnel was required to talk securely with Rabbit.
I've been using Apache Qpid for some time and am pretty happy with it. Unfortunately I get the feeling that development on the draft 1.0 spec has fizzled out. It's kind of a chicken and egg scenario with developers not wanting to implement a spec which is still in flux and the AMQP workgroup not wanting to ratify a spec which doesn't have at least two compatible implementations. I really hope this isn't the case and we'll eventually see the 1.0 spec ratified, because right now compatibility is kind of a crapshoot with different vendors all implementing different pre-release specs.