The Neo Freerunner is being developed along with the OpenMoko Linux project to create a fully open phone/Wi Fi device and the accompanying Linux Operating System for it. I think FLOSS should be used wherever possible and I love the idea of a fully open phone.
I don't appreciate companies that use FLOSS in their devices yet restrict the user from doing anything, thus showing a lack of respect for the community and philosophies of the software they are profiting from.
The Freerunner works fairly well as a Web Device. There are a variety of Web Browsers to choose from. I currently use Minimo when I want to surf from my Freerunner.
I want to use it as a WiFi SIP phone as soon as there's a decent client written for it (the idea of using it as a SIP handset for the computer is interesting to me as well). :)
Ideally it should be running a SIP client with SRTP/ZRTP capabilities for secure communications.
Supposedly you can get linphone to run on the Freerunner, but I haven't tried yet.
There are of course several GPS programs available.
TangoGPS is quite nice for general GPS usage and information.
Navit and GPSDrive are both available for routing, though I haven't really tried that yet.
Wardriving/Warwalking! (or just plain Wireless LAN mapping/troubleshooting in general)
(Come on, admit that you've all been thinking the same thing!)
Unfortunately the chip or driver for the WiFi doesn't support monitor mode, so no luck there.
However, you could hook up an external WiFi card and use that for kismet (I believe there is a kismet port).
ATT Prepaid is working well for me so far.
I am playing with several Document Readers such as Evince and FBreader.
Mplayer with the pythm pygtk app for controlling it works quite nicely.
My OGG collection is a bit under 4GB as I recall. I have an 8GB card in my Freerunner. :)