There are at least 3 situations that can arise with CC licensed works that can be quite disturbing.
1. A content creator releases something with a CC license, then dies. His family takes the website offline and then starts suing everyone that used his works, accusing them of copyright infringement. Copyright exists beyond the grave and the copyright now belongs to them. Unless you can prove you have a license to use the work, you will most likely lose the case and have to pay the family of the content creator. How will you prove you had that right if the site is gone? What if there is no copy of the site cached anywhere on the internet at the time you go to court? How do you, the content creator, ensure your family members won't be greedy after you die and go around suing the people you allowed to use your work? What can you do other than threaten to rise from the grave and haunt them for the rest of their lives if they do?
2. A content creator releases stuff with a CC-BY license. He blocks sites like archive.org from caching a copy of his site. He waits till people are using his content, then removes the CC-BY notice from his site and begins suing people for using his works. Or he changes the CC-BY to CC-BY-NC-ND and sues everyone that has used it commercially or remixed it into new works. If you can't prove the original CC-BY license, how do you defend yourself from a CC license troll?
3. You release a work but do not CC license it. Someone else comes along steals it, slaps a CC license on it, and puts it up on their site. Yes, you can sue him for doing that but what do you do about all those people now using your work that don't know the license was invalid?
I have actually had #3 happen to me. I posted a wallpaper on my website a long time ago. Someone came along and cropped it and included a portion of it in a scrapbooking kit, which they CC-BY-NC licensed.
After thinking about it for awhile, I came to the conclusion that even if I pursued the matter and forced the site owner to remove that piece from the kit, there was likely a lot of innocent people out there using it for purposes I never intended or allowed. In the end I chose to CC-BY license the original wallpaper and let it go. Unfortunately, anyone that had obtained the original kit won't be giving credit to me. They will give credit to the site they got the kit from. It's just a chunk of a silly wallpaper, no big deal to me. But what if it had been a book or music that someone else was being wrongly credited for instead of me or something I never intended to be distributed for free, something I created with intent to sell and profit from?
Here is the problem, the way I see it. There is no central database and repository (similar to the USPTO for patents) where content creators must register and deposit a copy of the works they intend to CC license. There are no registration numbers issued for each individual CC licensed work. There is no registration of use by anyone that wants to reuse a CC licensed work. Nobody is keeping track of all of this in one central location. Currently, anyone that wants to CC license a work just needs to slap a statement on it saying that it is. And anyone that wants to use it just needs to slap the same statement on it and link to the author.
If every content creator had to register each CC licensed work and get a registration number for it, then anyone that wanted to reuse that work would have a way of checking and verifying the license, which would continue to exist even after the creator's death. This would offer a lot more protection against scenarios 1 and 2. And if you had to register your reuse, it would offer a way for notifying those that used a work in good faith, in cases of scenario 3, that the license wasn't valid and they need to stop their use and/or distribution immediately.
Such a database and repository could also be good for the commons, if done right, by providing a searchable central archive of all CC licensed works, browsable by the public. It would encourage reuse far better than an author's obscure no-traffic website on some unspidered corner of the internet.