1. Conflicting Clients. There are a ton of clients, with the number growing all the time. Although they work on basically the same source code and protocols, they all install and operate as if they had exclusive access. They want to control the PC so that they are in charge of what resources are available. When multiple clients are installed on a PC, not only does that create confusion among users, its a “last installed, first in charge” approach. That approach and lack of respect for other clients will lead to user configuration problems. That’s not going to work. At some point they get considered to be malware and the clients will get uninstalled

2. End Users don’t understand how P2P works, and once they do, they get concerned about giving up bandwidth. Most users don’t know how to go in and edit the default settings. So even if they settle on a single client and are happy with just the content available on that network or to that client, they aren’t going to be happy about their bandwidth being in constant use to save a content provider money .

3. The P2P model of seeding is a HUGE problem for those using wireless broadband with bandwidth constraints or per bit or per minute costs. People are going to wake up and find that the provider a lot more than they ever thought possible because they installed a client on their Laptops. That could lead to these networks blocking the protocol.

4. There is a misconception that there is bandwidth savings for the end user. If you want to download a 1gb size file, 1gb of data will be delivered to your PC. There is no savings of bandwidth on the client side. In fact, the client is charged a bandwidth premium because after they have received the entire file, they are asked to participate in the peering by delivering parts of the file to other users.

This in turn becomes an issue to services providers, whether DSL, cable, whoever. If quite a few users on a network segment are seeding files, it can slow down the network segment..

P2P is a standard approach to network design that eliminates the need for dedicated servers. P2P is also a popular term for freely available Internet file sharing software systems.
Peer-to-peer (P2P) networking eliminates the need for central servers, allowing all computers to communicate and share resources as equals. Music file sharing, instant messaging and other popular network applications rely on P2P technology.
The P2P acronym has acquired a non-technical meaning as well. Some people have described this second meaning of “P2P” as “people-to-people.” From this perspective, P2P is a model for developing software and growing businesses that help individuals on the Internet meet each other and share common interests.

The emergence of P2P technologies in the early 2000s led to changes in both the law and how it is enforced. P2P technology allows individuals to connect directly with other individuals’ machines for the purpose of swapping files. Users who download and install P2P applications can share music, movies or any other files present on their hard drives. Although P2P technologies have become notorious as tools for copyright infringement, using a P2P network to share music with the authorization of the copyright owner is legal. In fact, many musicians have used the technology to promote their music.

However, sharing music on a P2P network, without the copyright owner’s permission infringes his copyrights. The reproduction right grants the copyright owner the exclusive right to make copies of his work. The distribution right ensures the exclusive right to distribute copies whether through sale, licensing, or lending. When music is shared via a P2P network, the person who downloads it is making a copy of both the sound recording and the underlying composition. And whenever a user downloads music using the P2P network, the uploader has effectively distributed a copy of the music.