I use Thunderbird with Exchange (admittedly IMAP for mail, but EWS calendars).
The real problem is the "just works" desktop (well, laptop) of OS X has skimmed off a lot of developers who would otherwise help GNOME by scratching an itch or fixing a papercut. What's left are the grognards who want to develop a desktop for everyone and have ruined it for the power users.
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