I can't for the life of me find a way to remove calendars... it seems, that for me that they are all shown, regardless of the visibility tick-box, and having subscribed to a very busy calendar, it shows all its events all the time. Without the option to hide it. I also couldn't find a way to simply delete a calendar. There is a 'plus sign' but no 'minus sign' in the 'calendars' dialogue (Ctrl + L).

I may be missing something obvious, but from what I see here, removing calendars seems impossible once they have been added!