Over lunch today I finally made time to read up on the Creative Commons CC0 waiver and how it differs from the public domain mark. In essence, CC0 is a universal waiver of economic rights (traditional copyright, but in some jurisdictions not moral rights) in a work you have created, whereas PD is a mark that identifies an existing work as in the public domain.
Therefore I have decided to use CC0 for my blog and other writings, not PD. (Why not just use the public domain mark? I haven't had time to research it fully, but apparently you can't just place something into the public domain in some jurisdictions; unlike PD, the CC0 waiver has a fallback license to handle such cases.)