I'm listening to WWDC2012 Session 707 on Bounjour. At 15:25 into the session, the apple engineer explains that you need to register your bonjour service name with IANA before publishing. I found that the link in the presentation does not work, and found this replacement:
http://www.iana.org/form/ports-services
Some of these fields look quite intimidating. Do I really need to fill out a service name request to publish my bonjour app?
In the interest of preventing every iOS developer going out and creating arbitrary (and possibly conflicting) service names and ports for their own applications, Apple rightly stresses that you should go through the approval process. Remember there are services on all kinds of platforms that depend on mDNS.
In practice, if you can find a port that's used by some extremely niche application that nobody's ever heard of, then you can get away without registering. The implication of this is that no RFC-compliant mDNS responders will recognize or honour the port or service name you're advertising as it's not part of the 'prescribed' IANA list. But as long as you don't create lots of unwanted noise (e.g. advertising your service as
_http._tcpwhen it is something else entirely) then you should be OK.