Haha I know that feeling. I've spent most of my time on this project working on the level editor. It lets you click & drag scenery props into the level, resize them, change the layer they're displayed on, set their type and special attributes and save it out to xml's that can be serialized directly into the game - and I'm quite happy with it. In game on the other hand my lemmings can still only walk & bash through some walls. I should probably work on them some more, alas we're approaching a deadline at work, so I tend to spend my lunch working on our title rather than my side project.
So how many people are working on something for this challenge?