Another Hitwise graph showing more disappointment for MSN/Windows Live - this time for Calendar. Since its inception in April, Google Calendar has been steadily gaining market share, while both MSN and Yahoo have been losing theirs. 

Interestingly, while both MSN and Yahoo gain most of their entries to their calendars from their mail portals, Google seems to have a more universal appeal:

"Yahoo and MSN calendars are primarily used by people who use their respective email services - Hitwise Clickstream reveals that for the week ending 12/30/06, 88% of the upstream traffic to MSN Calendar came directly from Hotmail, while Yahoo! Calendar received 48% of its upstream from Yahoo! Mail or Yahoo! Address Book, and the bulk of its remaining traffic from other Yahoo! sites. Google Calendar, on the other hand, received only 19% of its upstream traffic from Gmail for the week ending 12/30/06, and 42% from Google search."

We've been expecting to see the emergence of Windows Live Calendar for a long time now.  Jim Roos mentioned the Calendar team back in August, and in June, Oren Sreebny from the University of Washington posted a short list of features of a Windows Live calendar.

We're not sure what Windows Live is waiting for in coming out with their own calendar.  Certainly it's coming, and it may be tied in to some as yet unannounced new products/features.  But it seems like a bad idea to allow Google to take over the market, and then have to play catch-up in yet another category.  Hopefully we'll be hearing news about Windows Live calendar soon.