I think Freenet is great. It needs a bit more polish in the implementation, and improvement of some topology issues; but I find it very promising.
However, the model of Freenet is quite different from that of email. Email--including anonymized versions--is a party-to-party system on a push model. The sender actively directs a message to an intended recipient or recipients. Freenet, in contrast, is pretty much the same as the web: one publisher, many (unspecified) receivers, with a pull model.
It's not that one is better or worse, they are just for different things. I had considered discussing Freenet, but decided that what it did was simply different enough not to warrant inclusion in this particular article.