I don't know if there's a better place to submit this but I was noticing 404 errors on a couple of images (loadingAnimation.gif and tb-close.png) from the thickbox media uploader on the p2 front page new post form.
By default the media uploader uses relative paths starting with
../ because it runs inside wp-admin/. The fix, since WP 2.8.4 is to override the location inside p2's post-form.php :
Oh also, I'm using WordPress 3.1-alpha from the SVN trunk and a SVN checkout of the p2 v 1.1.5 tag/branch.