I know nothing about WP7 but I have experience with windows pocket pc, ppc2002 wm2003, wm5 and wm6. There is the same alarm bug from the first ppc to the wm5. The problems with activesync are the same in all those editions. Every new version has significantly LESS features than the one it replaces. Things they removed include: wifi syncing, sketching in pocket office, handwritten notes in contacts etc.
Input is so dated (no fullscreen kb, no internationalization) and the plugin system for new input methods is probably buggy as every 3rd party input app I have used hangs the device up. The UI and browser are exactly the same since 2002 making the vendors create full replacement shells, a thing that creates unnecessary redundancy - and confusion "why the contacts app is different when I launch it through the messaging app?", "why do I have 2 menus?" Microsoft should dictate the hardware, because there is a history of WM running in underpowered devices (ti omap 850 200mhz) and causing user frustration. I hope all these are new in wp7, but seeing where ms is heading to, I don't see enough innovation on their behalf, just trying to maintain their monopoly on the desktop systems, and using that to get users buy their other products too. Still many people see my N900 and ask "Does it run Windows Mobile?" and when I say "of course not" they turn around disappointed. And again what's their marketshare? near-zero.
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Well, it's good to hear that Microsoft has managed to make a useable UI, but after looking on some of the pictures and videos, it is quite weird to me.
Look at this image. My problem: the "screen" is so much bigger than the display resoultion that the big captions just don't fit. So in a menu, only 3-4 letters of the title can be seen at a time, which is in my opinion quite annoying. I like the panoramic desktop idea of Maemo 5 much better!
microsoft for the first time does seem to have produced a great mobile OS UI. I do think a lot of people will buy wp7 devices. I for one want to keep my n900 for atleast couple of years. Let touch screen UIs develop and mature