We use zeromq internally at dotcloud, and it's an absolute pleasure to work with. There is that weird obsession with asserts, but a lot of the problems we had with rabbitmq are gone.
That main reason doesn't apply only to zeromq, though; with google's protobuf you can write an rpc layer on top of pretty much any channel in ten or twenty lines of code.
ZeroMQ is not a serialization or RPC mechanism, but a smart routing system for packets of data. It doesn't even include one. Many people use google's protobuf with ZeroMQ.
As a relative newb, seeing what ZeroMQ can do had me slapping myself in the forehead. I wish I would've known about this when I was gouging my eyes out trying to build my own abstraction for ExactTarget's terrible groups system.
I just got done watching this video while sitting at a coffeeshop, and it was super useful, as I'd just started using 0mq on a client/server for testing fuzzing.
Nada. He just compared one of his sample APIs to redis. Don't have the exact quote, but it was something like, "this does a few basic things, similar to redis; put, get, etc."
http://zguide.zeromq.org/page:all