Patents are being given out like candy these days because it's up to the person applying to show the patent examiner all "prior art" -- and once the patent office is given notice that someone else had previously described in public the same thing, the patent has to be rewritten to cover only what is uniquely new.
There's a big business online now in bounty payments to people who can dig out the prior art to invalidate patents issued due to lack of knowledge by the patent examiner of what's already out there.
Anyone who's described a device or modification in public, here or elsewhere, shouldn't be too worried by a subsequent patent issued to someone else for something similar.
Just remember if you get a "lawyer letter" that lawyers are like prize fighters -- they expect to get into the ring and try really hard to knock the other guy down with the first punch, and they expect the other guy to block that and counterpunch very hard, and at THAT point they recognize each other as professionals and set about having a slugging match.
Remember that when a lawyer walks up to an ordinary person and throws the punch (letter, first draft offered of a contract, whatever) -- it is a MOVE in a GAME to figure out how strong the opposition is.
Never, ever, just fall down when that happens to you -- talk to someone knowledgeable about legal matters and find out if you need to hire your own gunsling, er, lawyer, to throw the block-and-counterpunch.
Usually once the lawyers know they are both in the ring and reasonably well matched, you get a negotiated outcome.
In particular, patent law is like that -- someone applies for and gets issued a patent for "bright things that light up" and sends you a letter saying you can no longer make yours -- in response, you challenge the patent by showing prior art exists. So you have to establish that the Sun rises in the East every morning, for starters, and there is other prior art as well, to limit the scope of their patent.
