I'm no expert, but I'll give a go from personal knowledge and experience :) I guess peer to peer networks are usually more reliable - if one peer out of 70 goes down, there are 69 that can still work. Having many peers is also more reliable because of the geographic locations of the peers - instead of having a server in New Zealand and a downloader in England, you can have many peers spread all over the world. This allows peers to always have a faster connection, no matter where they are in the world. Peer to peer is also a bit more anonymous. You (and the Great Firewall of China) don't know who runs the other peer computers, apart from their IP addresses. That presents a factor of security, where one peer can potentially feed malicious files to the other peers. Another advantage is that P2P networks usually have a bad reputation (i.e. Torrent networks), and so ISPs do throttle or limit internet connections that have many other connections or are using torrent protocol, regardless if the service is legal or not. For example, torrenting open source software is totally legal, but my ISP still tries block me from torrenting Ubuntu, sometimes. One factor, that I can think of, of unreliability, is that when a P2P network isn't advertised, the peers who want to download only have one or two uploading peers to connect to, or in some occasions none at all, instead of dozens or hundreds. The fewer peers there are, the more likely it is that the connection will be slower than a server based network. The fewer peers there are, the more people will go to other peer networks, and stop using the old network, and eventually the old network is abandoned.... Until someone with the original set of data decides to advertise it again. That's why it's a good idea to keep torrent services running in the background in order to keep the networks going. They did you a favour, they expect you to do a favour back ;)
