We keep digging into theming the Forums area of the site. We've done good so far, but the deeper we dig the more difficult things are going to get. Partially just because I don't have a ton of experience with Vanilla Forums and partially because it's just kinda weird!
We're trying to create and customize some sidebar modules, like the top right one, where we welcome new users and provide existing users a place to log in. Right away we struggle with which files output what and how. This is troubleshooting at work! We essentially echo out some content in different places and see where it ends up on the rendered page.
We eventually get it going and the login button works! Our wireframes and UX instinct is that having a login form right in the module itself would be the best way to handle login. Essentially a "static" login form, instead of the default way Vanilla handles logins, which is in an Ajax'd in popup. We can't just re-create the form markup ourselves because the login form has fancy tokens and stuff that help security. We're going to have to decide if we want to go to battle here and figure out how to make a static login module, or just roll with the default pop-up way and style that up to our liking.