Yep. Outlook killer is a great way to put it. I guess Google tried to do that with GMail, and Google Apps for your Domain, but only managed to kill off Exchange (in small businesses). GMail still suffers from many of the same issues as Outlook, in terms of collaboration (though it did solve both the spam and the storage problem). This is a more complete solution that has a chance of replacing Outlook because it's just a lot better.

Then again, Microsoft doesn't need to ditch Outlook - they could just release Outlook Wave - after all, it's all open-source. That would be nice - we'd all win from such a move.