Isn't it impossible to place work into the public domain? Nope

I remember reading Lawrence Rosen's article and had always assumed he was correct that there was no way to "place" a work in the public domain. Here's Rosen's recent admission:

"I admit that I have argued for years against the "public domain" as an open source license, but in retrospect, considering the minimal risk to developers and users relying on such software and the evident popularity of that "license", I changed my mind."

For a practical application of abandoning your copyrights, see http://unlicense.org/.