Here's another idea to have a lot of lists at your disposal, just not taking up large amounts of space on your tabs of lists. It also is a nice way of organizing lists.

The idea would be to create a higher level above list called List Group that would contain a group of lists. For example, you could have a list group called Contexts and another called ContextsUrgent. The first would contain a bunch of context-specific lists, the second a bunch of lists that were similar but with the added filter of due very soon. Both these groups could sit on your tabs of lists as "Contexts" and "ContextsUrgent" and they could either have some dynamic fold out that you could click on a specific smartlist (eg @workurgent) in a way similar to a dhtml cascading menu, or you could have a little icon on the tab that would signify it's a group and hitting it would expand out all the submenus.

Ok, sure, this is probably not going to happen any time soon. It involves a good deal of work, both on the backend and front. But I thought it was a cool idea anyway ;-P