IMHO there is no handheld device, nor is there likely to be one, which does the whole job for GA preflight tasks.
I can get very basic weather data on my phone, but can't run any usable route planning app on anything that size.
One needs something bigger - a 7" screen or similar. Obviously not a phone, PDA or anything like that.
The Ipad is good for nothing other than a PDF browser - IF you can get a load of plates printed off to appropriately sorted PDFs. That's a possible EFB solution for IFR pilots, which are a small group.
I have played with loads of gadgets but no matter how I look at it, a
small lightweight laptop is the way to go. With a GPRS/3G radio (which can be a bluetooth-connected mobile phone**) it
actually does everything.
Funnily enough the Ipad's advert budget and fashionable following should result in a load of lookalikes from China but they will be normal 80x86 computers and thus far more useful.
The big issue with WM is that M$ do not offer any support or patches. They delegated this to the device manufacturers, who obviously washed their hands of customer support. Compaq, HP, Toshiba, Fujitsu, etc, never supported these products, giving rise to a raft of online forums where thousands of p*ssed off owners moaned about issues, and occassionally found fixes. This killed the PDA market well before "smartphones" came along.
We now have "convergence" of phones and PDAs (and low quality cameras) but I don't think this is relevant to GA preflight activities. In limited situations, a "phone" can be used to get taf/metars or even meteox.com radar data and such (my compact Nokia E51 can) and that is OK for a preplanned route, but flight plan filing is not usually a standalone task; one needs to plan the route somehow, with Eurocontrol validation if IFR, and all this extra stuff needs a laptop. So being able to run AFPEx on a phone is of use to some people some of the time, but usually only if they skip a lot of other important stuff.
** the advantage of using one's phone as the GPRS/3G radio is that you already have a SIM card in your phone, which you presumably "look after". Having another radio in the "portable device" is just a PITA because it's another SIM card to keep topped up, etc. Also many people have phones provided by their employer which is even better
