Kazaa is "technically" decentralized. It has a key server for verification and updating of global supernodes. If the verification server is taken down the only thing that happens is the whole username/PW scheme is skipped (bs waste of time anyway) and the supernodes are not updated.
But this does not matter, as Kazaa upon connection failure will just search through every availible node in it's list of supernodes, and any other attached nodes it has cached. (if you want to see this in action just load up your firewall such as norton and watch it search through connections while logging in)
So Kazaa does have a central point right now, but if that central point is taken out it won't make a difference other then adding connection time to the first load of kazaa. And now that kazaa won in court overseas that set a pretty powerful precedent that will cause trouble for the RIAA or anyone to shut it down heh.
And please don't bring up the whole morpheus fiasco, thats involves something completely separate from centrality and involves a company dispute. in fact if you want you are still able to use morpheus contrary to belief