Ok, I just dug through a bunch of UK law. The most relevant bits are here:
http://www.publications.parliament.uk/pa/bills/lbill/2012-2013/0089/2013089.65-69.html#r005 or search that page for 116A which is the relevant section. Or just search for the phrase orphan works.
It sounds nice on the surface. If you can't find the copyright owner "after a diligent search" then the UK government can license the work on a non-exclusive basis, essentially treating it as public domain. Do what you want with it (if you are in the UK). One problem is that the Berne Convention says copyright is automatic upon creation. If it's not yours, tough, it won't be out of copyright for 5 generations or so. This gets around that.
So yeah, it authorizes UK folks to copy and profit from your stuff if the copyright owner can't be found "after a diligent search." The specific regulations aren't detailed yet, that will take a few months.
This would pretty much apply by default for pictures uploaded to image hosts, or fiction that you post anonymously, or even an old web page at the internet archive that points to an abandoned email address. Possibly abandonware too.
It's open for abuse, since stripping ownership info from a digital work is trivial. You can't tell when things were added to the web, so it becomes retroactive by default. It adds a layer of legal protection to UK companies that rip people off. Maybe the detailed regulations will sort all of this out, but right now this is a mess.
What can you do? Tell people about it. Don't panic, and don't cause panic. Just mention it and link to the relevant articles. If you want to avoid your stuff getting ripped off, don't post it to the web, same as always.