Thanks for the links.  I didn't realize that the wtfpl and the unlicense were actually public domain dedications.  I had thought about using the cc0 previously, the main advantage of which is that it falls back to a permissive license in places where that is necessary.

I decided against cc0 because it a much more involved license and I think that disallowing disclaimers of copyright is absurd.  Where are these jurisdictions, really?  And if someone used my public domain software in these jurisdictions, who would they face legal threat from?