As far as stability goes, I have only had to hard reset my device once due to a weird system failure, that I was not the cause, in all my years of using the operating system. I have however owned a few problem phones like the Cingular 3125 and the Motorola MPx220 that would suffer due to hardware problems/malfunctions and there has been a few time when installing a 3rd party application kicked my phones face in 8 ways from Sunday. Both of these problems however weren't due to the stability of the operating system but due to the stability of the hardware or the programing of the 3rd party application that caused the error.
Stuff like this happens though when you have programs and hardware developed by 3rd parties. You can't expect every developer to put in the same time and care into testing an application as you would expect Apple or Microsoft to do (key word, expect
). I'm sure there would still be problems even if Microsoft took more aggressive control over Windows Mobile and started developing their own devices, but there would hopefully be a lot fewer and more far between.