I don't know if Android would take that large of a chunk out of Blackberry's user base. It will probably draw away Pearl users and small-businesses, but Blackberry's core market (medium to large enterprises) will probably stay on that particular platform. Exchange integration is great (for the 95% of companies that use it), but as far as I am aware, on Blackberry with BES and WinMo w/ SCCM have true central management capabilities that enterprises want.
As you put in your post, Android will probably have the biggest effect on Palm, especially since they've seemed to tie their fate to Sprint. I can see Palm being bought out by RIM in five years or so. It will also be the final nail in the coffin of Windows Mobile, but that shouldn't be a surprise as Microsoft has been licensing ActiveSync to any mobile software developer that wants to pay for it (there is even a Blackberry implementation of it).
Apple will probably be hurt more than people realize, and the Android platform will play a small part in it. The iPhone is a great product, but in the United States, it is restricted to AT&T's now overburdened network while the Android "platform" will be available on most carriers in some form. I don't think that many iPhone users will switch to the Android, though, but it will attract many potential Apple customers who were holding out because they didn't want to give any money to AT&T.