Bukkit

I'd love for a setting to make you invisible to the mob matching your head.  For example: Wear a zombie head and zombies ignore you.

There's no status I can set that says "I'm still deciding if I'm going to add this or not", so I'll change it to "Waiting" until I decide. I like the idea, though.

A very nice idea (in my opinion). ;)

As much as I like the idea, I think it may be out-of-scope for the plugin (which just provides head drops, doesn't add other mechanics).

However, it's entirely possible for an addon-plugin to use PlayerHeads API to detect mob heads on the player and possibly change mob behavior (though I don't know how hard that second part is).