An interesting though brief patent interference case concerning flat-panel solar concentrators. The plaintiff (Morgan) had filed a continuation patent application, which is a means of getting additional claims out of a previously-filed specification. The new patent gets the same priority date as the old one, so you don't have to worry about later art (such as that of the competitor whom you want to pay you royalties), but you don't get the usual 20-year patent lifetime. Morgan then came after Banyan.
These concentrators are made by gluing together complicated sheets of plastic which have reflecting and guiding structures inside, so that the light comes in the flat side and goes out the edge of the sheet. That means you don't need as many expensive solar cells. Banyan, whom I was working with, had managed to avoid the asserted patent claims--all except one, which I had to tell them was a direct hit. Of course that ended my usefulness to them, but that's how these things go; the lawyers are advocates for their clients, and the expert is an advocate for the facts. That's a privilege.
The bright side of all this is that the review board awarded priority to the defendant, so it all worked out for our team in the end.