The only downfall I can personally see is battery life, but that should be no worse that any average smartphone. So if you rely on your phone heavily for work, buy a spare battery and charger and you'll still be good.
The only other thing I can see is the size etc, it may be too big for some, but that's a personal choice. Check out videos on youtube etc to get a sense of exactly how big it is in the hand. For me, the size is manageable.
For connectivity and Exchange etc, the windows experience is unbeatable imo.
I guess the point is that I don't really see any major downfall
