I've used Unlicense before, but I have since been persuaded that this was a mistake. Frankly, I think that unlicense inadequately protects user freedom. It does not contain a patent grant or estoppel. While I don't care about attribution, the disruption of provenance is problematic. I should hope that there are few companies interested in shipping code that, as far as they can tell, fell off the back of a truck.

Suppose that Foo Corp releases Unlicensed code that includes patented material. Baz Ltd goes on to develop a widget that uses Foo's code. Later on, Bar Inc buys Foo Corp and files suit against Baz.

No disrespect meant to Arto, but he simply isn't a intellectual property attorney. (Edit: And neither am I.)