Today Google released Calendar to Beta, which as
Jason pointed out, is like a regular release to any other company.
Could this be the end of Outlook for many companies? I can envision a Google appliance, similar to their search box, that combines the power of Google's hosted email service, with the new calendar service. You pay 3-4k for the box, it sits on your network, chugging away doing mail and calendar, instead of an Exchange server, plus the per seat charge for Outlook. Sure, the calendar features might not be as polished as what Outlook/Exchange offer, but I'd be willing to bet that at least half of the smaller bussinesses that use Exchange would gladly trade those lesser used advanced features for the cheaper goodness of a Google box for calendar and mail. They get to keep their data on premise, or in a location of their choosing, not having to give it up to Google's wishes.
Will we ever see this, who knows? But if we do, you heard it here first.
--JOsh