Answer:
At this time, we do not recommend releasing software using the the CC0 public domain dedication.
Creative Commons Zero is a legal device known as a "public domain dedication". It is essentially a statement of intent by the copyright holder to waive copyright ownership in the work — that is, the copyright holder wishes to place the work into the public domain.
Because such a waiver is (perhaps surprisingly) not possible in all jurisdictions, CC0 also contains a "Public License Fallback" clause that goes into effect "should any part of the Waiver for any reason be judged legally invalid or ineffective under applicable law". The fallback is essentially a copyright license that is very similar to an Open Source license, in that it gives up most of the restrictive powers associated with copyright, and allows redistribution and modification of the work.
In February 2012, Creative Commons submitted CC0 to the OSI for approval as an open source license, requesting that the OSI evaluate the public license fallback section, since the rest of the text is a waiver of rights rather than a license. An unexpectedly intense and detailed discussion followed — search for "CC0" and "Creative Commons Zero" in the subject headers of the February 2012 and March 2012 archives of the OSI License Review mailing list.
CC0 was not explicitly rejected, but the License Review Committee was unable to reach consensus that it should be approved, and Creative Commons eventually withdrew the application. The most serious of the concerns raised had to do with the effects of clause 4(a), which reads: "No ... patent rights held by Affirmer are waived, abandoned, surrendered, licensed or otherwise affected by this document.". While many open source licenses simply do not mention patents, it is exceedingly rare for open source licenses to explicitly disclaim any conveyance of patent rights, and the Committee felt that approving such a license would set a dangerous precedent, and possibly even weaken patent infringement defenses available to users of software released under CC0.