Faster Update Cycles
Add requested features with smaller updates instead of larger updates that add lots of features all at once.
If it was just Microsoft, it would be easy, but it isn't. I can only imagine the nightmare Microsoft had trying to co-ordinate all carriers worldwide for Mango. If they start adding more updates, it'll get like Android, where different carriers, and different phones are all running different versions.
2 updates per year seems to work pretty well, and the roll out of Mango shows they seem to have done a good job.
I do hope that even the first party apps, are truely apps, so while we may have to wait 6 months for the next OS update, its possible to update 1st party apps more reguarly.
2nd that.. this way Microsoft can teach the users what the new update is capable of.