TBH, MS solution is the greatest one I've ever seen. Integrated email, calendaring, group based notifications, phone system, IM integration... it works great. You can even call your voicemail to get your emails read to you over the phone! (or schedule a meeting in a similar way, automatically putting it in your calendar)
There's one "but" - you have to go MS all the way. You cannot use those features without windows and their web ui is a complete disaster. That's one of the reasons it should never be used at any technical university IMHO. As soon as you touch anything MS, you're in the area where standards don't apply.
I tend to agree. I came from an Exchange background, and went all around trying different alternatives. There's nothing out there that quite compares.
I'm currently using Zimbra, and it is good enough, but it just isn't as nice. And "good enough" isn't really good enough. Whoever wants to topple Exchange is going to have to do better than this "me too" crap.
How about actually integrating the contacts, tasks, schedules, and email in some intelligent way?
As loathe as I am to admit it (and I still won't recommend or adminster it) Exchange is reasonably decent for the end user. You need to keep a sacrificial Windows install/VM for the rare cases you need an Outlook-specific feature but most of the daily functionality is accessible from other clients.
Between Thunderbird and a Blackberry I only really dip into Exchange to set new filters anymore.
There's one "but" - you have to go MS all the way. You cannot use those features without windows and their web ui is a complete disaster. That's one of the reasons it should never be used at any technical university IMHO. As soon as you touch anything MS, you're in the area where standards don't apply.