We rolled out the new site theme for Mathematics. It is live now.
What new theme?
If you're like, "What the heck are you talking about?", then you should read the Meta Stack Exchange post entitled Rollout of new network site themes (and maybe the posts it links to for the full background).
Your help needed
You are one of the first sites to get a new, unified theme. I previously posted the designs for theme in meta. The feedback given to that post was considered prior to rolling out the theme. Please help us look for issues/bugs and post the details (including images where needed) as an answer below.
If you have concerns or issues regarding the left nav then this Meta Stack Exchange post is the right place for feedback. If you have issues with any functionality that is unrelated to the new theme, then please post a new question.
As you see, the team working on this theme design is seriously studying the criticism here, and responding to it. Editing this to allow anyone so inclined to change their vote.