I first came across the technique around 10?? years or so ago from a big discussion on the HBD, where it was the latest 'Big Thing', it has been around for much longer than that and some German brewers had rediscovered it in some research of Narziss (IIRC). What the report showed was that in blind taste tests, drinkers were able to identify, and in fact preferred, the FWH beers consistantly. Sensory evaluation reports from the tasters were that the beer had a more rounded mellow hop profile and aroma. Of course what happened on the HBD was that everyone took it to assume that if you first wort hopped you beers they would have a good aroma.
The technique is fairly simple, you take your aroma addition and add it to the kettle as you start to run in the wort from the mash tun. the hops then sit around in the wort and the hop aroma is magically fixed with the more concentrated malt sugars, and this survives through to the final beer. Well obviously that proved not to be the case, and there were a lot of unhappy brewers around.
I found that it didn't give me massive hop aroma, BUT, I did notice a change in the hop profile, a more mellow bitterness, which I liked, and even better this carried over even with extremely harsh copper hops (like Target). I therefore use a modification of the process and add my High alpha bittering addition as first wort hops, and carry on using a flavour and aroma addition as before . . . Well not quite, I now add my aroma hops when the wort in the boiler has cooled to below 80C, and in the couple of trials brews so far (That have supposed to have an intentially big hop nose) the results have been very promising.
One important trick of FWH though is that the FW Hops must sit in the wort at no more than 80C until the boiler is full then you bring it up to boiling. You loose the effect If you start heating the wort as soon as the boiler element is covered.
Like all things this technique is not a 'silver bullet' that will make a massive difference to your beers, but once you have nailed the major factors down , it is one of those that will allow you to reach that little bit higher on the quality scale.
As for the science about how it works, I really am not even going to try to make a guess, I have a couple of theories about some of the things that are going on, but without access to a brewing lab with a HLPC Gas Chromatograph there is no way of knowing whats going on, and even with one you really are guessing at the reactions behind the scenes.I lost my access to such a lab a long time ago, and the brewery is now sadly demolished (I don't even think the name lives on
). Still it does sort of mean that my interest in the brewing process is now a lot more practical even if I do suddenly disappear into the stratosphere with some of my more esoteric theories 
Comments and Criteques welcome
