The problems with public domain dedication across jurisdictional lines, as I understand them, are:
1. Users (who are aware of how the law works, in general terms) in a country that doesn't recognize a right to relinquish copyright to the public domain will be afraid of getting sued, so they won't use the software. It might as well not be open source for them.
2. Contributors to your public domain software from those countries are not allowed to relinquish copyright in their works to the public domain, and as a result you're actually accepting work under copyright into your otherwise-public-domain software, which means it's not really public domain software any longer, because of mutual copyright observance agreements between those countries. Thus, for instance, because the US recognizes German copyrights, and Germany doesn't allow dedication of copyrightable works to the public domain, a German contributing code to a public domain work in the US actually contaminates the public domain work with code covered by copyright, thus making it no longer a (pure) public domain work, even in the US, because of US recognition of German copyrights.
If the German in the above example actually transfers the copyright to you, then YOU dedicate the work to the public domain, that might work. I'm just guessing, though, and I'm pretty sure it would require some explicit legally binding (and provable) statements about transferring copyright to you.
To make this more complicated, in Germany copyright is not transferable at all. The best you can do is assign exclusive rights to someone else (doing that correctly is non-trivial). Even worse: There are some rights that belong to the creator alone and they cannot give them away.
edit: Please stop advertising for AL2. It's not as good a license as people think. It contains some fiddly terms that many people don't even know are there, or don't understand, and is distressingly easy for people to casually violate by accident. Its complexity adds to the problem as well, by offering many opportunities for unintended legal effects in (so far hypothetical) future lawsuits to arise from interactions between parts of the license, a problem with any long license, and AL2 has severe license incompatibility issues as well.
It is not certified by either FSF or OSI. The process of getting it evaluated by the OSI and certified involves a lot of money, unless it is such a popular license that the OSI is politically backed into a corner about it. The FSF's politics around such things get downright strange; I'm not even sure what it would take for the FSF to consider a non-GNU license.
AL2 contains restrictions such as a requirement to perform bookkeeping when making changes (notes for every modified file about who changed it) and restrictions against changing another file. The bookkeeping restriction is violated with stunning regularity; so far, nobody has been sued over it, as far as I know, but that's true of the majority of license violations anyway.
AL2 also, as I mentioned, has some serious license incompatibility problems. Some patent and indemnification material in AL2 is considered incompatible with GNU licenses prior to v3, for instance. In fact, any license that includes a restriction against any connected work being "more restrictive" in some way (which includes GNU licenses, among others) is likely to suffer some significant compatibility issues with any license that has weird quirks like the previously mentioned issues of AL2 (bookkeeping, invariant file), too. The patent termination part of AL2 is unlikely to cause incompatibility with most licenses (GNU licenses are weird, in that regard) unless they come with a restriction on "restrictions" and have a less restrictive patent clause than AL2 (no patent termination, for instance), but the edge cases in AL2 can cause issues with other licenses.
I'm not a lawyer (and this is not legal advice), but I think a case could be made in court that AL2 and GPLv3 are actually not compatible at all, because of those clauses, despite what ASF and FSF say.
Beyond that, there's just the simple fact of complexity. You've probably heard that software tends toward X bugs per Y lines of code, and that's true for the most straightforward, linear software designs. As the complexity of the design of the software increases, though, the possible unexpected interactions between parts of it increases as well. The result is that, in practical terms, the likelihood of bugs actually increases faster than the number of lines of code. The same effect occurs with legal licensing terms, to some degree; the more complex a software license, the more likely you are to run afoul of unexpected legal effects of the license. AL2 is a rather complex license, much simpler than GPLv3, but significantly more complicated than something like the COIL, especially given the inclusion of the terms I mentioned earlier, which are radical departures from the most widely-used, best-understood "state of the art" of license design.
Red Hat is a business. FreeBSD is a volunteer/community project.
FreeBSD is a volunteer/community project that offers more business-friendly licensing than gNewSense, which is also a volunteer/community project. It is not, however, a business like Red Hat.
Red Hat development gets all that funding because Red Hat is a business. FreeBSD relies more on volunteer time because it is not a business.
Fedora is a "community" project of Red Hat. FreeBSD is a community project of, well, a community. Red Hat funds Fedora (astroturf project) as its testing ground for RHEL (commercial project), while FreeBSD is just a community project.
THIS IS NOT LEGAL ADVICE.
The problems with public domain dedication across jurisdictional lines, as I understand them, are:
1. Users (who are aware of how the law works, in general terms) in a country that doesn't recognize a right to relinquish copyright to the public domain will be afraid of getting sued, so they won't use the software. It might as well not be open source for them.
2. Contributors to your public domain software from those countries are not allowed to relinquish copyright in their works to the public domain, and as a result you're actually accepting work under copyright into your otherwise-public-domain software, which means it's not really public domain software any longer, because of mutual copyright observance agreements between those countries. Thus, for instance, because the US recognizes German copyrights, and Germany doesn't allow dedication of copyrightable works to the public domain, a German contributing code to a public domain work in the US actually contaminates the public domain work with code covered by copyright, thus making it no longer a (pure) public domain work, even in the US, because of US recognition of German copyrights.
If the German in the above example actually transfers the copyright to you, then YOU dedicate the work to the public domain, that might work. I'm just guessing, though, and I'm pretty sure it would require some explicit legally binding (and provable) statements about transferring copyright to you.