We're currently using a primitive method of adding gateway messages to our live streams by adding items to the metafiles. I'm starting to research better solutions, and I'm interested to know if any of you out there use a service such as Ando Media (saw them at IMA a couple years ago), or if you continue to "roll your own."
We are actively looking for a good enough (and cheap enough!) solution as well. CDNs make it a bit more complex. If you run your own streaming server there are several software solutions out there but I haven't gotten to testing them yet.