From basic observation I have seen execs moving from BlackBerry to iPhone & Android because the latter platforms are in fact now both capable of syncing reasonably well with Exchange.
BlackBerry is still a powerful platform for corporate email but they're mostly used for reading - rather than writing - email so the data entry & ergonomy for basic email operations isn't *killer* enough. On top of that new >200 DPI screens on Android & iPhone devices make reading much more pleasant. If you read a lot, then having hardware keys to scroll (I love being able to use space to page down on BB) is great though, but the text resolution is shit.
The thing most have missed so far is that the gadget that is invading the boardroom is the iPad. Meetings where everyone has a slide deck on their own tablet make sense, especially when (if indeed it isn't already out there but has escaped my attention) a collaboration tool allows slick collective annotation on iPad.
Many apps on BlackBerry are pretty awful, and my all-time favourite, viigo, was bought by BlackBerry and then almost instantly killed. It relied on a proxy to format RSS properly and serve it to the terminal, and the proxy never works any more. The new RIM News Reader app isn't available in my country. WTF? It was the only app that allowed RSS + Twitter (multiple accounts) + stocks + weather in one easy place.
Note also that the processing power on smartphones make BlackBerry appear exceptionally slow. RIM are going to lose, unless they bring back something a bit more *killer* in the corporate space. They have some interesting niches though, esp. for teen texting where BlackBerry does come into its own. iPhone text messaging is way sexier though, mostly thanks to the higher DPI.