Whoa, 400+ posts! To me, 20 posts is too long already for navigation. The first/last arrows help, but I also would like arrows for previous post / next post. Maybe also for previous ten posts / next ten posts, if there are more than a hundred posts.
A great option would be to turn off images. Or at least to turn off gratuitous images. Users should specify when they attach an image, whether it is important for conversation, or it is there just to liven up the post.
I would also like to have in-Cake recents stack. So, I am reading one thread, then jump somewhere else, then somewhere else, and then I can jump back to the first one. There should be a menu, tracking my recent threads, which would bring me back to the same post I was reading. On a big screen this can be implemented on a sidebar, so my current thread would be in a wide area, and my "background" threads in the sidebar. Not sure about the UI for a smartphone.
The bottom bar. When I am on the homepage or browsing the topics, there is the bottom bar for Home / Recents / Search / Mentions. I like it, it is useful. I wish it were shown when I read a thread.
The bar that invites to make a new post first looked ambiguous to me: where this post will go? Ok, it goes to the current thread without quoting anyone. But for the first time it was not clear, maybe it should have better be linked to a thread visually.
The edit link on a post: first, thanks for unlimited edits! For a long, um, essay-long post it is a pain to scroll up for the Edit link, I wish it was floating beside the post.
When replying to a post the complete post that is being replied to goes into the hidden quote or whatever it is called, that can be clicked and opened. If I also manually quote by copy/pasting and formatting a specific portion as a quote, I get the same text twice. It would be nice if I could select a portion in someone's post to quote, and this portion would be emphasized in that hidden quote element, which would save me from manual quoting. This won't work for multi-quote though.