Some days ago I installed WordPress 3.0.1 successfully. But I faced a boring problem. When I trying to use the drag and drop widget on sidebar it would not work. I thought that some plugin may be create drag and drop functionality problem. Then I have searched on internet for a solution and found some effective tips for this problem. Mainly it is the java script problem.
First solution: De-active all of your active plugin. Then start activating plugin one by one and checking drag and drop works. It is the easiest way to find which plugin is culprit.
Second Solution: Disable Accessibility Mode, Screen Options ( below the Logout link on your admin panel) > Disable accessibility mode. Now check your widget drag and drop working.
Third Solution: If you are still in this problem, you must do this. It is the great and must solution tips. Just install the Google Libraries plugin and amazingly that seemed to fix the problem.
Now go back to your Widgets panel and try to drag and drop your desire widget on sidebar. I hope it will working and free you from this type of odd problem.