There are a couple things I'd like to see implemented which I think would help improve the site UI.

First, I'd like the ability to ignore image based sigs.  Most are annoying  and others are just downright offensive but they make reading the forums a real pain.

Second, I'd like to see the ability to allow game based themes to override my preferences for the UI (I'm a subscriber) if available.  Some of the game specific UIs are rather nice looking and it woudl be kind of fun to see them every now and then.  It might be even nicer to add game specific themes as options for subscribers to choose for their UI.