[tsimionescu]

Yes, it doesn't matter for determining if you are infringing on the patent. But it does matter for (a) the kinds of damages that you can be liable for, and (b) it can matter if you try to attack the patent itself to try to get it invalidated. Patents are only supposed to be granted for non-obvious ideas, so one way of attacking a patent is to show that many people came up with that idea independently, which is a strong argument that the idea doesn't pass the non-obviousness test and can get the patent invalidated.

[freejazz]

Yes, they can be evidence that invalidates a patent if they qualify as prior art.