Over the years I have experimental WP sites setup for testing things out today I have tried one-click upgrading from a few earlier versions which are all OK, e.g. from 1.5.2, 2.0.2, 2.0.4 and 2.0.6 etc. In my last few upgrades I even got aggressive without deactivating plugins and reverting to default theme.
Keep up the good work, WordPress team!
PS: I also solved the get_links vs wp_list_bookmarks problem, see this thread.