Oh jeez, I really hate how my country works sometimes...
In manner of US law as I know it he is rather heavily skirting the law. It is illegal to upload/share/seed/host copyrighted material without permission. What he did was merely link to other sites(and by sounds allow his users to add links as well, though any website with some method of posts/comments users can do this as well) and also make ad revenue from visitors. If he himself actually followed links and used the resources he and his users provided then yes he violated the law as I know it in the US. If they argue solely that he provided a means to find and download material illegally, then it can be argued(thought not very strongly) that any search engine also hits this area unless they filter/report such results, for what more empowering way to allow people to easily find illegal data then to search almost the entire internet?
However, he is a citizen and resident of the UK, if they have similar laws, he shall be tried in a court over there. If not, then he did not violate the laws of the nation he lives in and should be left be. If this is the case, extradition is complete bogus, for he may have violated US copyright laws, but those laws don't apply to every single person with an internet connection around the globe, if it did the pi...'that giant torrent site you know of' would be long gone by now.
On a random tangent from that, if our laws are to be applied to anyone who uses the internet, then the laws of other nation's apply as well, and that is just asking for not only an entangled mess, but imagine the laws some random country would pass and say 'ah, but its our law and it applies to internet users world wide!'. Yeh, crazy I know, but if it is so for the US then it can be applied elsewhere. I wonder how long until the US gets extradition demands for news reporters...
*edit* Few things that just popped to mind... If he ran a website that linked to who knows how many illegal sites and services, is the US seizing those sites as well? and why attack and demand extradition of the guy who compiled a website listing instead of those running the actual direct infringement? Also, unless the server the guy ran was in the US, how much of a grey area is it that there is no outcry of a US govt body seizing a foreign website? if it is a grey area go take over 'that giant pirating site'