Infact SSMS 2012 is better than 2008 and it is really worth the change
Some useful features
Usability : SSMS 2012 is powered by visual studio so the UI looks lot similar with Visual studio
I always have issues with 2008 intellisense (autofill) which is very slow and sometimes even manual refresh take longer time to refresh the metadata. But 2012 is very impressive and i am much surprised about the meta data management.
In 2012 intellisense accept part name search. E.g . If your table name is abc_xyz_ETL then you can type xyz which will pick all the tables which contains the xyz while writing the query
The new improved MDX query editor is very useful for SSAS testing.
New Source safe integration - the SSMS 2012 can be easily integrated with team foundation server with a free plugin. I am really hoping to see some free plugin for subversion soon.
Projects are easy to create and maintain
In built SQL Beautifier will help you to format your SQL quickly. This tool also comes with formatting options, so you can customize based on your organisation standard
Check this Blog