Great article, Michael - very informative, I'll be forwarding the link to my iphone-using friends.
Interesting that you compare its abilities to a full client, such as a proper web browser, along with the associated fallibilities. With great power comes great responsibility, eh?

Personally I've jailbroken mine, to allow third party apps. I have a SSH client on there, with full CLI access using MobileTerminal. Obviously the first thing I did was change passwords from default on both the root and mobile accounts. I also generated RSA keys and swapped public keys with the Mac I use at work to allow simple, secure comms.
Since connection via USB is only of any use when using iTunes (Apple created a proprietary communications protocol that prevents any machine actually seeing the iPhone as attached storage), I use STFP over port 22 to communicate with my phone. This allows me to swap data between it and any machine wirelessly and fairly easily, though Wi-fi isn't the fastest medium.
There is an app to allow wireless sharing via the AFP protocol - this lets the device show up in Finder. The only problem with using a GUI (as opposed to a terminal or FTP connection) to browse the device is that the filestructure, like OS X, uses symlinks at the top level, and I've experienced problems with the Users directory disappearing when I've tried to access it. This doesn't happen when using FTP or Terminal.
There are some other really useful third party apps I use regularly, which fully justify the act of jailbreaking the device for me. There's a rich, if dilettante, development community out there.