My favourite feature of Exchange 14 has just been announced: full support of Safari in Outlook Web Access.
Right now, in Exchange 2007 and earlier, Safari doesn't support the full OWA experience. You get the light version of OWA, which is admittedly pretty good for Exchange 2007. But if you're a heavy Exchange user like I am, the lack of goodies like tasks or categories really hurts. (Remember, I've been able to sync these with Exchange since I began using internal builds of Entourage for Exchange Web Services several months ago.)
I'm sure that as I get an opportunity to use it more, I'll find more to love about it. It means that I don't have to drag my laptop everywhere with me to have great access to my Exchange account, I can use one of my Macs at home and get it all. Right now, though, getting my tasks and categories is what I want the most.
This makes my iPhone the odd one out. I do love my iPhone, but I hate that my calendar isn't properly colour-coded there with my categories. I hate the inability to get my tasks and notes on it.