Upgrade Nightmare – No Posts, Permissions Issues and Can’t Create a new post

I had some problems upgrading to 3.0.3 on a multi-site installation. I had used the automatic upgrade and it failed, but luckily, downloading and extracting the new files from WP.org and uploading them directly fixed it. I would try that first. If that doesn’t work, try re-uploading your backup files. You did make a backup, right?