As Apple and Samsung have proved, everyone has some kind of patent on something -- which means that everyone could, in theory, sue someone else for some other feature that seems blindingly similar to their own feature.
It all comes down to how much money you have, how good your lawyers are, and what moods judges and juries happen to be in.
When Facebook introduced the "Like" button, it seemed so thoroughly obvious that you couldn't believe someone hadn't thought of it before -- a 5-year-old in Bangalore, for example.
Now, a patent company called Rembrandt Social Media has decided it holds the patent for, well, liking things online and a few other aspects of Facebook.
As the BBC reports, Rembrandt holds patents that it believes contain within them the original and legally binding idea for what seems like much of social networking.
It claims that a Dutch programmer called Jozef Everardus van Der Meer registered two patents over which Facebook has ridden in the same manner that it enjoys riding over all kinds of other social norms -- meeting in person, for example.
Van Der Meer -- who died in 2004 -- was the creator of Surfbook, something that had, at its heart, Facebookian tendencies.
The complaint, which has been filed in the U.S District Court in Virginia, says that Van Der Meer's idea constituted a "personal social diary" on the Web.
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The plaintiffs claim that Facebook "bears a remarkable resemblance, both in terms of its functionality and technical implementation" to Van Der Meer's personal diary.
You didn't think Mark Zuckerberg was that clever, did you?
It's unclear why it's taken quite so long for his heirs to act legally, and I contacted Facebook to see whether it might have any idea -- or even a comment. It did not.
However, as Ars Technica points out, one of the claims now is that Facebook knew about Van Der Meer's patents, because in a patent issued to Facebook in 2012, one of them is mentioned.
Rembrandt's lawyer, Tom Melsheimer, told Ars: "To describe it in a general way, he had the notion of being able to publish and share information with a select group of people and the ability to link in other types of information. It was the beginnings of what we would say is social networking."
Rembrandt is seeking "reasonable" royalties until 2021.
I would like some reasonable royalties too, as I put a personal diary onto a computer in 1998. It described my feelings about snow, my liking for Polish pierogi with cabbage, and a peculiarly tall Russian girl called Svetlana.