Mobile view - this needs major rework and a dedicated mobile theme. Right now it's practically unusable to type as the keyboard is taking up 95% of the composer box. The voting buttons are too small and things basically don't look right for anything but browsing. Other buttons to attach pics are equally too small. Needs mobile specific features like 'take a pic'.
The composer in mobile view is a serious issue, it's barely usable in the current form. Just a pair of lines show up, depending on the screen size. Isn't there a way to fill the screen with the text area without resizing it when popping out the keyboard?
Geotagging is also very cool and innovative. I see a lot of uses for it, think about combining it with an event plugin.