There are numerous ways to get around the large file problem: that it's impractical and often impossible to send large files to other people via e-mail. One of the most unusual is AllPeers, which works inside a Web browser (Firefox only).
AllPeers installs a buddy list pane in Firefox. It's very easy to kick off file transfers to people on the list; you just drag files or links from your file window or from inside your browser.
The file transfer technology inside AllPeers is BitTorrent, which means your files aren't uploaded to any central service; it also means that if you're sharing a file with a group of people, the bandwidth to transfer the file around will be shared by all, potentially speeding up transfers. Some people will be able to download your files faster than you can upload them (this discrepancy is the norm on almost all consumer-grade broadband connections).
The big downside of AllPeers is that it requires that the people you're sharing with also use the AllPeers Firefox extension. Unlike several other file transfer systems, there's no quick way for a recipient to get the file without first installing this application. This precludes casual file sharing, even though it's not a bad setup for friends or coworkers who constantly share files.
Why limit file transfers in this way? AllPeers founders Cedric Maloux and Matt Gertner told me that since applications are moving to the Web, it's logical to conclude that the Web is also the right platform for file sharing and that the browser the right interface. But if you send somebody a link to a file, it's a leap to expect that they'll install a deeply embedded Firefox extension just to see it. (The extension, by the way, cannot be turned off, although it is easy to uninstall.)
Maloux and Gertner also want to make it possible for consumers to sell their files (they expect to roll out a commerce system in about a year). Again, requiring users to install an extension to complete a transaction will likely put a damper on sales.
Fortunately, AllPeers is working on a way to allow some functionality to be shared with people who don't install the extension. This future capability is based on the neat change that AllPeers makes to your Firefox browser: it turns it into a server. As Matt Gertner wrote to me, "We're planning to add the capability to publish items as normal HTML so that they can be viewed from any browser even if AllPeers isn't installed. I could imagine a P2P blogging app based on AllPeers."
AllPeers' technology looks strong, but at the moment it's in too small a box. The download capability needs to be accessible to people who don't want to install the Firefox extension.