Yahoo! is rolling out the first major overhaul of its web-based calendar application in 10 years. But while there are 278-million Yahoo! Mail users, only about 8 million people use the calendar.

The new Yahoo! Calendar beta looks pretty nice. It has a slick interface that lets you zoom in on any particular date for a close-up even when you're using the month view. The calendar also features Flickr integration, so that random Creative Commons-licensed images can be pulled in to make the calendar look pretty. Eventually users will be able to add images from their own Flickr accounts.

The updates aren't just cosmetic. You can manage multiple calendars, share calendars with friends, and create to-do lists associated with your calendar. The new calendar also supports iCal and CalDAV protocols, which mean you can import calendars from AOL, Apple, Microsoft, Mozilla, and Google. At least in theory. I tried importing my Google Calendar with no success. But I was able to import my Yahoo! Calendar into Google, so that's something at least.

Keep in mind, the new Yahoo! Calendar is still in beta. And it shows in a couple of places. There are a bunch of features available in the old Yahoo! Calendar that are absent from the new beta, including the ability to search for events, show sports, ifnacnce, holiday, and weather information, or even add symbols for event types like birthdays and anniversaries. You should also note that if you switch to the beta version of the calendar and then decide to switch back, you will lose any changes made in the beta version.

Long story short, the new Yahoo! Calendar is worth checking out. But you might not want to make the switch just yet. The beta is only available to users in the US, UK, India, Taiwan, and Brazil and the moment, with a worldwide rollout expected within the next few months.