Freenet works very well for sharing large files. For example an mp3 album only takes a few hours, and a 700MB movie can be easily downloaded in a day.
It does depend on how popular the files are, and how much bandwidth you allow Freenet to use, but these figures are realistic even for a minimal bandwidth setup.
And the more people that are downloading something, the faster it will go, as it gets cached around the network.
I2P doesn't do data storage like Freenet.
I2P only encrypts and anonymises the transport. It's up to you to host the services on your machine. I2P just means people can use those services (e.g. a webserver) without knowing who is hosting them, and without you knowing who is accessing them. IF you go off-line, your service goes offline too.
Freenet, on the other hand, does have an encrypted and distributed data storage layer. You can go off-line and your website will remain available.
What you describe sounds very similar to Freenet.
Freenet is pretty much the only anonymous P2P system that includes an integrated, encrypted, and distributed data storage layer. The others like Tor and I2P all require that you host your data on a specific machine and it is just access to this data that is anonymised.
A weakness of this approach is downtime of your secret site can be correlated with downtime of your server e.g. during power cuts, etc. A benefit is that dynamic sites are possible using server-side languages.
I think you have your facts wrong.
It's true, if you are a Tor "exit node" that proxies to the regular internet, you will be at risk of having your IP address associated with illegal websites. But most people don't do this.
Standard use of I2P or Tor will put you at virtually no risk whatsoever. You are just routing encrypted traffic of which you have no idea of the content.
The Freenet anonymous forum software "Frost" is spammable, and has been under prolonged repeated attacks for some time, so it is fairly unusable.
Use the Freenet Messaging System (FMS) instead. It is a decentralised and highly spam-resistant anonymous forum system, using a web of trust. It has an NNTP interface, so you can use a regular newsreader to read and write messages.
(That is another Freenet link, you need to have Freenet installed for it to work.)
Freenet is quite usable at the moment, and there is a fair amount of file trading going on. It can easily handle whole albums in a few hours and DivX rips of movies in a day or so, depending on popularity.
Once you install it, download the FMS (Freenet Messaging System) application, which is like anonymous Usenet, and make requests or offer uploads.
The benefit is that no-one, not even your ISP or government agencies can see what you are uploading or downloading.
It is also designed to be very difficult to censor. Currently it uses UDP for communication between Freenet nodes, with no real fingerprint to the traffic, so it is difficult for ISPs to filter without affecting things like VoIP or gaming.
Should UDP filtering become more prevalent, it will move to another form of transport, ultimately ending up as steganography, where it disguises itself as some other encrypted protocol.
Freenet uses similar techniques against spam on the Freenet Messaging System (FMS).
Two things are mentioned in the article: many eyeballs, and moving to a pull technology from a push one.
FMS uses a web of trust, similar to PGP's to rate the trustworthiness of users, and this makes it simple to do collaborative filtering of spammmers (many eyeballs).
It also uses a pull technology, where each user has their own message queue, and you poll the queues of people you trust. There are tricks to make this scale up, so you don't have to be polling millions of people all of the time.
Initial entry to the web of trust is done mainly through a captcha system, although it can be done through any out-of-band method. Even if the captchas are defeated, which they will be regularly since this is an arms race, the first two steps should mitigate the damage done, by rapidly spreading bad trust values for the spammer to other users before they get to downloading their messages.
It works well in practice on a small scale, but obviously there are neither the numbers nor the dedicated spammers to test it out properly.
If anyone wants a challenge, please come on Freenet and try to spam the Freenet Messaging System!
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