Sorry if you already did! but the advice is to avoid upgrading to wordpress 3.0 if you strongly don’t need the exclusive features in it.
Try to avoid upgrading to the new version at least 2 or more weeks (better if you could wait until the end of summer) as one or two security releases will be out by then.
WordPress 3.0 is really beautiful piece of script but security is a major issue with all these fresh releases. Those who are too much excited to test it out are advised to do it on a test install and not on their live server or if you are too out of control to test it on your live site then please make a backup of your site. However please bear in mind that it’s not necessary that once you are hacked you are aware of it too.