The todo-list allows you to filter and search by summary, tags, and priority, but not (easily) by the calendar to which the task belongs. To do this, you have to uncheck the calendars you don't want to see displayed. This is tedious if you have multiple calendars and want to quickly restrict your view to exactly one, and you have to recheck them all if you want to switch back to your calendar and see your agenda. You can also sort by all of these, including the calendar, so the information seems available for filtering already. I'd prefer an interface where I simply click the calendar in the Calendar Manager sidebar, and the tasks in the todo-list are filtered to only that calendar, but I imagine a filter similar to the tag filter (where I can select the calendar in a drop down) would be easier to implement.