Customizing the SharePoint 2010 isn't a walk in the park. Working with the XML files using CustomActions, CommandUIExtensions, CommandUIDefinitions, ... can get a little annoying after a while, especially if you're re-deploying your feature after each change. While customizing the ribbon today I encountered a very frustrating problem with the ribbon customizations. For each change I made in the Elements.xml and deployed to SharePoint it was as if I didn't change a thing. After numerous attempts I even decided to throw away my customizations and use some I found on the web (from Chris O'Brien) for example.