I just upgraded from an old b2 install, mostly for the multiple / sub-categories. I'm really not interested in RSS, Ping Back, etc. One thing I would like is a way to simplify the (write / edit) interface. I'm thinking a set of check-boxes across the very top as to which fields on the page to display, so stuff I never use (Slug, Password, Excerpt, etc) isn't taking up space. Yes, I know I can just delete them from the page myself, but I thought it would be a nice general feature (and, suppose I wanted to keep the features available for rare use).
I could probably tackle this myself, but it would require some new db entries, which would require changes to the install scripts, etc.