Lianchen: This paper (pdf warning) from the St. Louis Fed might interest you. Related to patents specifically rather than IP generally, but rebuts the "innovation" point using Econometrics, which I personally find fun as a former student of the discipline. Anyway, money quotes:

A closer look at the historical and international evidence suggests that while weak patent systems may mildly increase innovation with limited side-effects, strong patent systems retard innovation with many negative side-effects. Both theoretically and empirically, the political economy of government operated patent systems indicates that weak legislation will generally evolve into a strong protection and that the political demand for stronger patent protection comes from old and stagnant industries and firms, not from new and innovative ones. Hence the best solution is to abolish patents entirely through strong constitutional measures and to find other legislative instruments, less open to lobbying and rent-seeking, to foster innovation whenever there is clear evidence that laissez-faire under-supplies it.

And

Economists fought for decades – and ultimately with great success – to abolish trade restrictions. It will not escape the careful reader that patents are very much akin to trade restrictions as they prevent the free entry of competitors in national markets, thereby reducing the growth of productive capacity and slowing down economic growth. The same way that trade restrictions were progressively reduced until reaching (almost complete) abolition, a similar (albeit, hopefully less slow) approach should be adopted to “get rid” of patents.

As a side note, I'm someone who has previously supported IP rights but no longer do. In hindsight, I think the word "monopoly" was pretty key in accelerating my conversion (as in "the government should not be arbitrarily granting monopolies to private corporations"). Not sure why, but there is just something about that word that can really offend one's liberal sensibilities. I'm also not a huge fan of the board game, but that's probably unrelated.

-Shay