Because of AIA (America Invents Act), firms may now defend themselves against "junk" patents through filing Inter Partes Petitions with the US Patent Office. Unfortunately, this is expensive and most cases end in settlement which encourages further infringement filings by "trolls."
The Science magazine article suggests creation of a mechanism ("advance screening") to weed out low quality patent lawsuits.
Expert witnesses need to be aware that their clients may be on either side of such a dispute. I suggest that decisions about accepting cases require knowledge of the parties and law firms involved through similar advanced screening by a prospective expert.