We've said it a bunch of times here in the past when describing the life cycles of tech companies: when you're young, you innovate. When you're old, you litigate. We've seen it time and time again. The big tech companies that are no longer innovating and are far removed from their former position as major players in the market, make one last grasp at relevance by breaking out their patent portfolio and beginning to sue. The latest to take this death knell step appears to be Yahoo, which is threatening to sue Facebook for patent infringement. This may be a sad end to the legacy of Yahoo -- a once innovative company that has made pretty much all the wrong moves over the last half-decade or so, that is now left to snipe at those more innovative and nimble.