You're not the first; I have that problem, too. It's a minor miracle if my horn works. When I get aggravated enough, I'll make the dealer fix it, and I'll let you know what they say. Like I said, I can make the horn work by playing with the horn relay, but it's just a temporary solution.
Thinking about it, I can feel the relay click, so I don't think the relay is bad, but it could be. I'm leaning towards a bad connection in the PDB. I would think it would be easy enough to test with a continuity tester running from the output leg of the relay to ground--when you honk the horn, it should light up the tester. Getting to the bottom of the PDB to make the connection is another story entirely.
From what I understand, to get to the horn(s), you have to remove the shield that goes from the bottom of the valance/bumper cover to the crossmember, but I haven't gone there...