Would anybody who knows more about P2P tell me please what the download speed in this kind of file sharing depend on?(What are the factors?)
any answers from users and developers are fully appreciated

From user, there's something affect torrent download speed. I'm not sure about other P2P, so just about torrent.

- Number of seeders, the more seeders your torrent got, the faster you can download (Assume all of them don't limit speed). This usually go with torrent age, usually older torrent has got fewer seeders, while new/hot torrent got more.
- Location of seeders, the more seeders from your ISP, your country, the faster you go. Although, that isn't important if there're enought seeders in the first place (Say, your ADSL maximum speed is 2MB/s and you already downloading content @2MB/s then more seeders doesn't raise speed up anymore). And it's affects my speed because I live in a small country in E.Asia where cable connections to worldwide not good enough, so the local ISP seeders take big place. In developed country, this affections maybe less than, even not at all.

It mostly depends on amount of data uploaded by other peers.