The distinction between copyright and trademarks was my point. When you say "intellectual property," you're lumping together a bunch of things that aren't alike. (Also, if we do abolish all intellectual property, my crappy Gentoo computer with the aluminum case not only looks like an Apple iMac, it is an Apple iMac — just not the Apple iMac you're thinking of! Trademarks exist to prevent namespace collisions like this.)

As for the Molinari site, I looked at it, but it was very hard to find anything noteworthy in the wall of links with anchor text like "Copyright is murder," "The War on Copyright Nazism" and "On the Subject of Genocidal Rage." If you have a good piece in mind that argues against the historical utility of copyright, I would be interested to read it, because I've never seen such a thing.

And yeah, I think that there is a case for trademarks as distinct from other forms of IP. I think I'm on shaky ground here according to other market anarchists, but I think that trademarks serve a purpose of communication.

That is, that there is in reality a distinction between my 'iMac' and an iMac made by Apple, that trademarks exist to facilitate the communication of that distinction to customers, and that it's reasonable to deal with trademark infringement with force.

Of course, that opens an entirely new can of worms: what constitutes a trademark? The Apple logo? The shape of an iMac? The colour? Etc. etc.

No-one said this was easy :)

http://www.mises.org/journals/jls/15_2/15_2_1.pdf is a good start. It does reiterate the point that I'm trying to make, too, that utility is as bad an argument for IP as it is for slavery.