I just finished upgrading MacMegasite to Drupal 4.7. The upgrade was quick & painless. I had already installed the modules, made a few patches (most notably redirecting the feed to FeedBurner) and tested everything with a back up of the database from several days ago. To do the switch, I disabled posting, dumped the database, restored it to a new database, ran the upgrade script & configured it. I then switched the new directory with the old site directory.