Imagine this... you search for an event - your favorite band's concert in your city, a public hearing, your second cousin from Poughkeepsie's birthday. When you find it, with a simple click you add it to your own calendar. That's one of the great potential benefits of calendar standards, which we could do today, except that web authoring tools don't support the iCalendar standard. It's hard enough to get calendar vendors to support it, so that's not unexpected, but it is pretty simple to do.
All that is necessary is for the web authoring tool to create a small iCalendar (.ics) file for each calendar-type event, and add an anchor tag that references that file. Actually, iCalendar files can contain multiple events but let's keep it simple for this discussion. Then when a user clicks on the file, it is opened in whatever application supports .ics files (MIME type "text/calendar"). It works with Apple's iCal program, and I hear with Outlook (I don't have Outlook so I don't know for sure). It currently won't work with Palm's Desktop program, because that only supports the older and outdated vCalendar specification.
Here's an iCalendar example with a small add-to-calendar icon:
Watch Dick Clark (iCalendar)
And for Palm Desktop users, the vCalendar version
Watch Dick Clark (vCalendar)
Try one of them, and see how it works for you. Now, imagine doing that for any event information that you now have to copy and re-type into your personal calendar - wouldn't life be easier?