As the others already mentioned there are already a couple of P2P clients out there used comercially.

One good web site on your discussion is

http://www.peertal.com/

which is a page for "Business and Technology of Distributed Network Systems" in their own words. There you find a lot of interesting news what is going on in P2P development in the business sector.

I think one has to mention Groove http://www.groove.net, which I consider as one of the leading P2P products that are developed at the moment. Also the web page there gives qu
ite a lot of interesting information on the subject also numbers how much money could be saved with P2P technology in company networks.

I hope this is what you look for and that I could give you some new information ...

If I am wrong in some things please correct me =)

In my personal opinion I think there are quite some indications that P2P networks will survive. If they will be based on the Gnutella protocol as it is today? I doubt. I think the tremendous number of P2P network users that came up in such a short time shows how important and useful these networks may be/are. I say "may be" 'cause file sharing (Mp3, Movies, ...) is shurely not the long time goal and the only thing you can be done with P2P networks.

I am happy to discuss that a little bit more here, also the business models that can be though of, since once in a while people will like to earn money or not loose money ... not only Napster showed this (of course there have been other reasons - I don't want to discuss that here).
.
Hope I could help & Cheers

Felix