After playing around with WP at nerdfilter.com I have some thoughts.
1. More comments in the code would be greatly appreciated. A listing of where some of the .php files get their html from would be helpful.
2. A shift to common terminology like Preview instead of Advance editing.
3. Disallow same level users from editing each other's work.
4. Enable a static rss file. Generate it every few minutes and let the various RSS readers just pull the static file.
5. Performance could be tweaked. Not sure how, but WP is a bit resource intensive. At least on my hardware.
6. Less branding. WordPress at the bottom of the page is classy, having it at the header, at the login, etc its not.
A lot of this stuff is subjective so take it as such.