Definitely a sign that Yahoo stopped getting profit from doing anything useful, since they fell so low as to use software patents litigations for their income.
Apple, Google, Samsung, Microsoft and many others who are "getting profit from doing anything useful" sue each other every other month.
Yahoo didn't engage in software patent aggression before. So whatever the case, acting as a software patent aggressor shows deterioration of company ethics and usually signals that they can't compete on merit.
Except this lacks in both grace and providing the company with any innovative, competitive, long term solutions, and definitely sets it in a bad light. I don't see any benefit to doing this.
Maybe yahoo is pursing this goal.... with their schizophrenic product line (they once had two competing photo sharing sites under their banner and three social networks), I can imagine that they are worth more as separate parts than as a single undirected company.
Or... they can organize themselves as a traditional conglomerate.
These are good moves only in the short-term. Either Yahoo is flailing, or it's setting itself up for sale. Lots of good folks who work there (some of whom I know well)... I hope they're prepared.