The US Supreme Court reversed the Federal Circuit on one of the tests it had unstintingly imposed on parties in previous years on the defense of obviousness. One defense defendants try to raise in patent litigation is to argue, by clear and convincing evidence, that the patent is invalid because the invention was "obvious" to those skilled in the relevant art at the time the invention was made. The Federal Circuit had posted a bright-line barrier to this defense, fondly known in patent circles as the "TSM Test."
The TSM test refers to the Federal Circuit rule that the defendant must show an explicit prior teaching, suggestion or motivation to use a combination of previous references (publications) which could have been used to arrive at the invention, thus making it "obvious."
The Supreme Court did not reject the TSM Test, but it did reject its being the only way to prove obviousness, in KSR v. Teleflex, 550 US __ (2007). Instead a more flexible, implicit, commonsense (and vague) set of principles will now be recognized. For example, one would look now for "an apparent reason" to combine the references, whether explicitly suggested or not. In other words, a "motivation." The analysis for finding obviousness, however, still needs to be made explicit rather than conclusory.
The KSR case has had an immediate effect in patent enforcement. Whether or not it has changed or will change the ultimate analysis or results in patent cases is open to question. What is far less debatable is this: it has inspired nearly every recently accused infringer to raise with heightened vigor the argument that the patent in question is invalid for obviousness.