Re: So my choice is...
Well, you can still buy ink, fountain pens and paper :)
No, your option is a simpler one. Inform yourself of all the factors that matter to you and then make a choice that fits YOU. This is why interoperability is so great: for everything you do, you choose the gear that fits your needs, budget and risk profile.
This means you build a backbone focused on interoperability and then plug in whatever you need. I personally also prefer to use IMPA/SMTP/CalDAV and CardDAV rather than Exchange but for some that is a bridge too far. Your accountants like Excel on Windows? Fine, but make sure they save in .xls (not .xlsx - avoid the "x" formats as the bubonic plague they are).
Your designers are far more efficient on Macs? Fine - that is quite happy talking all manner of RFCs including SMB, and off you go. A bit of platform diversity also protects you from a complete cascade meltdown when another ILoveYou virus lands, or when someone codes an effective drive-by virus for a Mac or Linux box (that it hasn't been done yet is no guarantee of the future).
Want to go Open Source all the way (even if not entirely Free)? No problem - your backbone will support it.
Even before Sir Berners-Lee defined the URL idea we were already working on interoperability (which was easy then as most of it was Unix based). It's one of the most valuable features of the Net - make sure you keep that feature alive.
Biting the hand that feeds IT
