Old school: Lucent v. Microsoft
If you want an indication of the extent to which legal battles can drag on endlessly -- and drain the budgets of tech companies who should be churning out shiny gadgets for our amusement -- look no further than this epic struggle, which has been raging in one form or another since 2002, yet still made the Patently-O blog's list of important ongoing patent cases. It was originally based on a 1986 patent on data entry via onscreen keyboard that Lucent inherited from Bell Labs, and which Microsoft was found to have violated with a date-picker widget.
If that sounds like it should be scary for every smartphone and tablet maker out there, don't worry: the patent itself expired years ago. But litigation soldiers on, now over the details of the penalty Microsoft has to pay. Interesting points of law raised include the argument that, just because an application contains a patented innovation doesn't mean that innovation is responsible for the whole value of the application (as one judge put it, "There was no evidence that anybody anywhere at any time ever bought Outlook ... because it had a date picker"), and juries' right to assess the "obviousness" of a patent without too much kibitzing from judges on appeal.
Picture courtesy of Patently-O, from the patent filing
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