Microsoft arrogance aside: Gigantic, bloated, monolithic proprietary applications, written by a company known to be privacy-hostile and surveillance-friendly, handling your potentially sensitive communcations? I think not.
In corporate environment Exchange/Outlook is an awesome tool for e-mail, instant messaging, calendar, contacts, booking resources, etc.
I had to use Lync at my last job and to be honest it was one of the contributing factors to my leaving.
It breaks links, it breaks basic copy/paste functionality in clear and obvious ways, it wastes screen real estate like its going out of style, it's slow clunky and cumbersome... No Thankyou.
Lower TCO, has all the same features of Exchange (plus some collaboration features Exchange lacks), plus it's open source so you can hack on it or make your own custom modules if you desire.