Just updated to Drupal 5.2, but unfortunately not without problems. I didn't respect the advice from the upgrade guide to disable the clean url's so I got 404 (not found) codes for everything except the front page.

If this ever happens to you go to yoursite.com/?q=admin/settings/clean-urls and disable the clean urls. After that copy a clean settings.php file to your sites/default folder, modify the database and base url settings in it and run update.php. Log in through yoursite.com/?q=user and re-enable the clean urls. Now everything should be fine.

Hope this helps if someone has similar problems!