One of the criteria we use to judge intellectual property law is its effect on innovation. A recent study doesn't directly address this issue but it is suggestive because it says that only about ten percent of companies are highly effective in this area and that there are other ways than patents and copyrights to encourage innovation (link to NY Times article here
The complete study is here, together with a short bulleted summary. The key finding is "Patents generally don't drive profits. Boosting R&D spending can increase the number of patents that a company controls, but there is no statistical relationship between the number or even the quality of patents and overall financial performance."