While doing some upgrade tests with my development environment I came up to an org I could not upgrade to 2011 by importing the ORG_Database with deployment manager. My first thought was
Are there any unsupported JScripts inside, I should delete before performing an Upgrade?
So check your JScripts before upgrade
But even more important you should take a look at your plug-ins registered in Database.
If you´re not sure if the plug-in is compatible to 2011 you should better unregister this plug-in and all the steps before upgrading your Database to 2011.
If you´ve disabled steps – delete them before performing an upgrade
Doing so, I could solve my issues upgrading this ORG-Database. Maybe you don´t need this step in RTM, but you better take a deeper look at your registered Plug-ins in Database – It´s worth it.