I agree that the software is excellent, but that the lack of an ideal device is a frustration.
I run InFlight on a (now-discontinued) Fujitsu-Siemens PDA. This doesn't need hacking, and in-flight the setup works pretty well with the PDA mounted on a knee-board. However, a bigger screen would be a bonus. The major issue though is the user interface - having to use a pen of some sort to operate the device via the standard Windows Mobile interface isn't ideal (although not too bad on a kneeboard - I use my chinagraph pencil). In practice, this interface limitation means that you set up the route beforehand, and just use the device to tell you where you are. This in itself is of course very useful, but easier interaction while flying would bridge the gap with 'proper' GPS systems.
SkyDemon Plan can now be used inflight, so any sort of small notebook with a GPS dongle can be used - but again the standard Windows interface via menus, trackpad and keyboard leaves a lot to be desired.
By the way, there is a similar discussion ongoing on the other forum.