Okay, lemme shed some light on this issue. When you log in on to WP2.0, the server redirects you to the dashboard. At this point, the redirect is picked up by the browser and the browser starts loading wp-admin/index.php. After 20 or so seconds of waiting, the server *closes the HTTP connection* as if the index.php PHP script had timed out or something. This shows up on IE as the typical DNS error (and it's NOT a DNS error) and on firefox as a blank page, with the complete URL to it as the page title.
No warning, error or notice is printed on the Apache (or web server) log whatsoever, so finding the root cause of the problem IS SIMPLY IMPOSSIBLE.
I did notice that disabling my plugins and enabling them one at a time till I have enabled them all again fixed the problem... but only temporarily. The next day, things were back as usual - no access to the dashboard.
PLEASE WP DEVELS: HELP US, THIS IS DRIVING ME INSANE.
BTW, the Google Sitemaps plugin consumes tons of RAM, which causes the Web server (actually, PHP) to die when posting. So if you experience broken connections just after hitting Publish on the post editor, suspect the Sitemaps plugin.