While the interface of the Yahoo! Calendar is new, all of the features you enjoyed are still there, along with some enhancements. They have been announced that all users will be migrated to this new version of Yahoo! Calendar, and the current version of Yahoo! Calendar will be phased out entirely.
These are some of the key differences you may notice:
Updated Calendar toolbar: The toolbar that appears above your calendar has a new look and new buttons, but it still includes the same options to add an event or change your view (to Day, Week, Month, Year, or List view).
The new left panel: The new left panel includes three resources: a bird’s eye view of your calendar, a calendars list (which includes a list of your calendar “layers”), and your subscriptions list (a list of the calendars you’re subscribed to).
The new “To-Do” list panel on the right: This allows you to view the tasks on your To Dos list either all at once, or just those that are due or done. To change which items are displaying, click on “All To Dos” at the top of the pane.
Please note: Once your account has been migrated to the new Yahoo! Calendar, it will not be possible to switch back to a previous version.