Avahi often seems like a mixed bag. Sometimes it Just Works, but other times it doesn't---one of the big pain points of zero-configuration systems has always been opacity and difficult troubleshooting. For example, it's not at all unusual for well-meaning consumer network appliances to monitor and interfere with IGMP ("IGMP snooping"), ostensibly for performance reasons, but then unintentionally break mDNS. It can be very hard to figure out that that's what's happening when your printer just isn't showing up. In general distributed systems tend to be a pain to troubleshoot, but especially so the zero-configuration efforts since they often try excessively hard to be completely invisible.
