In re Bilski:

The Court of Appeals for the Federal Circuit (CAFC) has finally released their Bilski ruling. This decision reaffirms that business methods, and in particular, software programs are eligible subject matter for a US patent, dispelling some concerns that the court would set new guidelines for software, or perhaps rule that software was no longer patentable. 

The court instead, reiterated the Supreme Court ruling that business methods and software must meet the “machine” or “transformation” test.  If the invention is tied to a particular machine (not just a general purpose computer) or if it transforms a particular article into a different state or thing, then it is proper subject matter for a patent.  This certainly means that firmware for a specific controller would qualify, as would software that guides a saw to convert trees into lumber.  The court did say that a method or software that transforms data could qualify as long as the data represented specific physical objects.  So a method of inverting a matrix most likely would fail the test, but that same method used for structural analysis of a steel building might be considered proper subject matter for a patent.