The Calendar plugin displays links to the previous and following months in the html calendar. The problem is that these links are generated for every month, creating pages like Main/EventCalendar?month=-1258. This is bad for search engines, as they are trapped on the same page forever and ever and ever...
The calendar plugin should have a parameter telling how many months before and after it should display links to. For example, when displaying the table for ?month=-12, there will be no link to the previous month.