This was previously posted at the old forum, and would still provide great flexibility in using the module as a full-fledged menu.
__
I'd love to see the Category Listing items retain active status when selected so the module can work as a proper menu. There is a solution for adding this capability in Joomla's Latest News module that would probably be helpful in implementing something similar here, but PHP isn't my thing, yet.
BTW, I'm also using a variation of that article's recommendations to generate part of my menu automatically, and am very pleased with the K2 module's flexibility and the way it's going to save me a huge amount of time.
In case anyone is interested in a similar setup, it's just a matter of setting up a split Main Menu without adding the K2 categories. For each top menu level, create a K2 Category Listing Module with the same Module class suffix as the Main Menu module. The Menu Assignment should be to the top menu level item's page and any non-K2 pages in that section. Adjust the padding to fit the two menus together, and you get a hybrid, half-automatic menu that includes all the K2 categories and subcategories as they are created. Simple, but maybe someone could use the instructions.
(To anyone considering using the above - the category listing is no longer generating subcategories despite an option to choose the number of levels, so the above trick doesn't work so well now. Bug report will be in the appropriate forum.)