i recently updated this site to drupal 6.
it was a fairly delicate task.
i had to follow a few steps to make sure that the update worked ok. the first is to put the site on maintenance mode and to backup all my database, settings of the old drupal 5 site. then i created a duplicate "staging" site to test the new site with the new drupal 6 code. then i had to test each version 6 module and themes to make sure that it worked on the new site. once, i got that working, then i ported over to the "production" site. standard upgrade procedures i guess.
still, doing all this at night was not the best. the mind often doesn't work that well at night. lol.