Calendar seems to have a similar featureset to that of Outlook. You can put appointments on other people's calendars and you can schedule rooms, anyway. And, at Google, the conference rooms have motion sensors that allow the room reservation system to "garbage collect" unused rooms. (You also get an LED indication of whether or not you'll be running into someone else's time if your meeting runs late. Gotta love the hardware support!)

Can you expand on why?

* Update: Specifically for you, rather than in the wider sense; how does Exchange make /your/ life easier?

Works pretty well, actually. Calendar isn't perfect, but I personally prefer the UI to exchange.