Indeed, I used to demo it at the Linux SIG at one of my previous employers; unfortunately there isn't a good GUI solution.

I think it'd also be the worst of all worlds, the things the N800 can do well:

* Access the Internet, including IM and web browsing (let's not mention email & RSS here ;-))
* Play video and multimedia
* Quick, colourful games

The things an EPOC-running 5mx can do well:

* PIM (specifically Contacts, Agenda and Jotter)
* Data entry
* Office applications (although compatibility is a bit tricky even nConvert)
* Java (reasonably well, anyway)

The things a Linux-running 5mx can do well:

* bash
* vi

Bring on the Eeeeeee :-)