Over the last week, I've been getting the occasional meeting notification directly in Gmail and accepting the event places the event in my Google Calendar and returns a confirmation to the inviter. Gmail+Google Calendar is Outlook Web Access without the $Exchange$ server. I even created my own event, wow it was easy, and invited 3 friends. Google Calendar does to Yahoo! Calendar what Gmail did to the old Yahoo! Mail. It made it obsolete. Now, if only I could import my Yahoo! data into Google.
http://www.google.com/calendar/render
Oh ya! And they have an API.