As far as I understand, the stated intent of that proposal is to make "orphan works" less of a problem: If the copyright holder can't be identified, then arguably it should be possible to make use of the work, rather than just have it go into a kind of suspended animation where no one has the right to do anything with it ever.
When you put it that way, it's reasonable enough, but the fear is that LOTS of images on the web would easily fall into the category of "orphan", and it becomes hard to see how one could prevent people from grabbing any image they wanted, stripping the EXIF fields and any other metadata, and claiming that they found it somewhere and couldn't identify a copyright holder. There's supposed to be a duty of due diligence, but that's the kind of thing that's intrinsically hard to prove, and in practice it could end up meaning that anyone who can't afford a lot of legal fees can't really enforce their copyright.
I don't know how serious a concern this would really be, particularly in light of the complicated relationship between copyright laws in different countries.
You don't transfer your copyright ownership to a site when uploading, it's generally just umbrella licensing terms, not taking away your copyright ownership. Facebook for example, etc.
In any case, if you're paranoid, you could always legally sign over the copyright ownership to a legal entity you create, then license the images to yourself for usage (non-transferable license) (or even don't license, since the legal entity you create wont sue you).
You can then cannot legally license them yourself, only the entity can (which of course you control).
Similar to when people upload and share images from TV shows, celebs, or etc, they certainly don't own the copyright and cannot license it's usage to Facebook and others.
Tim Parkin has written an article about Orphan Works and the Enterprise and Regulatory Reform Act and how it could potentially affect photographers (article here) and I think that's what Clive's friend was maybe alluding to. Many social media sites strip out exif data when you upload to them - including Flickr (although only when the image is downloaded). The bottom line is, as I think was stated in Ian Grant's post about someone ripping articles, images and text off other people and using it as their own - if you want to protect your images from unfair use with no attribution or licensing fee paid to you as the creator - then don't post them on the internet.
Legislation is usually not the problem. The contract that you sign when registering at a site is. You have to read it carefully because it usually starts out with something that sounds very good but you will always find some small exception that is explained just at the end of the TOS that in short nullifies all the good things said in the beginning. In most of the agreements you are bound by the terms while they reserve themselves the right to change the contents without having to inform you of the change (just as an example I found this at the end of Google's TOS "By accessing and using Google Services, you agree to be bound by the terms and provisions of the TOS // which may be updated by us from time to time without notice to you"). You will find similar content in all TOS's.
Nobody wants to steal my work, should I be worried ?
Having negatives stored away affords great peace of mind. They can only steal pixels. Post online all you like.
The fastest way to devalue your work is to post it on the web, period....it *is* getting that bad.