Ubisoft will no longer distribute its new titles through Steam. So no Steam versions of Far Cry 4, Assassins Creed: Unity and the like.
It's interesting because they seemed happy to play both sides of the fence, unlike Electronic Arts. But maybe Steam is starting to see some splintering a la Netflix from major studios who realize that they can keep a lock on distribution and get 100% instead of 30% (or whatever their terms are). I personally don't care much -- I'll play FC4 on Uplay just as readily as on Steam and don't really dislike any of the major platforms. I'm sure other people will insist that now they'll never play FC4 (or AC: Unity or Dragon Age Inquisition or...) but I think the weight behind the titles will allow them to do just fine.