Google has released it's Calendar application, dealing a major blow to both Microsoft's Outlook and recent startup 30boxes, a strictly calendar online application. You can click here for a full tour.
I signed up tonight and I do think it's worthy of heavy usage. Some of the features include allows integration with other people's calendars, posting events for all users to see, and a variety of different time scales on which to view your calendar such as month, week and day.
Adding events is incredibly easy, due to heavy usage of AJAX, you simply click and drag the time your event is encompassing, and name it in a small pop-up. Wow. This, in hand with Google Finance, is the coolest Google offering I've seen yet. The user interface is top notch.
Count on Microsoft adding a product with similar functionality, most likely to it's already well diversed assortment of Live products.