I got a HOP hat from ebay (the one that's been floating around for a while.) It's still a good solid hat, but the text is more plain (not the original that Danny Boy wore many moons ago.) Still...it promotes the House of Pain, and I get a lot of comments on it.
The way I see it is this. If you see someone wearing a Slipknot t-shirt or something...it has basically no impact, because everyone's doing it (or Linkin Park or whatever.) How many people wear House of Pain gear? Especially in Cedar Falls, Iowa (where I, unfortunately, live.) It's unique around here, which is what I'm going for.