OpenURL has become, in a sense, the glue that holds the infrastructure of traditional library research together, connecting citations and full text. … [We found that] One-click (OpenURL) resolution was noticeably poorer [than Summon], with about 60% of requests leading directly to the correct fulltext item. More alarming, we found that, of full-text requests linked through an OpenURL, a large portion — 20% — fail.”
So… 40% of fulltext requests go to the wrong item? And 20% fail altogether. That sounds to me like a 60% failure rate.