Yea we did. There is a new dwg format ie. Autocad2007.dwg instead of 2004 or LT ect.
Depending on what version you're coming from ie 2005 or earlier you will need to learn how to customize the user interface (toolbars, custom commands ect.) they have drasticaly changed in 2005 into "Customization files .CUI" so u'll need to updgrade all your custom toolbars/commands.
Other than that nothing much new, from 2006 anyway.
Matt