Calendaring is my most important concern...
I'm pretty happy with my e-mail setup right now going through Gmail and BIS. Not sure what I would gain by adding the additional forwarding step of forwarding Gmail to my EMM account to check it that way...
Current Setup:
Gmail -->
(and keep copy in Inbox)
BB "From" address spoofed to Gmail. A copy of "Sent" messages from the Berry are BCC'd to Gmail (to keep the "Conversation" going in the Gmail interface) and filtered in BIS to keep from coming full-circle back to the 'Berry.
I can't see any benefit to going to this:
Gmail --> EMM Exchange Account --> BB
Am I missing something?
Anyway - back to calendaring... I've got email working OK, and my address book changes so rarely that it's only a minor concern. However my calendar is constantly moving around. I'm stuck with Outlook at work, but I like to use iCal at home. At this point, I'd be happy with Entourage (I know EMM is working hard on a solution for us die-hard fans of Apple!).
Let me know how you fare with GroupCal!