Originally Posted by commodorejohn
If someone puts something in the public domain, it's in the public domain.
"Public Domain" is not a clearly defined term, AFAIK. Especially not if you're thinking global - there's no real "Public Domain" in Germany, for example.
Just check some releases marked "PD" on Aminet, and you'll get a long list of different definitions, ranging from "send me a postcard" to "non-commercial". In the list I posted above, James Daniel's PD releases have this condition: "If you modify it, you let me know." Not a problem, you might think - until you realise the specified mail address is 20 years old *.
If you want to preserve code for posterity and enable people to use it right away, you should pick a well known license. Doesn't have to be GPL, if that's too viral for your taste - but it should be compatible with the GPL and be approved by the FSF and the DFSG. There's a wide variety of licenses you can use that match these criteria.
The 2 clause and 3 clause BSD licenses or the Creative Commons licenses CC-BY, CC-.BY-SA and CC-Zero are all perfectly good replacements for "Public Domain" - and they're well defined and everybody understands them.
* (I know James Daniels, of all people, isn't hard to find. Just giving an example of problems you might encounter)