Although at the time of writing UR12 is not yet released - I was checking though the changes in the latest SDK documentation.
In addition to the Ribbon Workbench being listed (yay!) I noticed the following statement about the getServerUrl function
"Deprecated. Use getClientUrl instead. This method is deprecated as of Microsoft Dynamics CRM 2011 Update Rollup 12 and the Microsoft Dynamics CRM December 2012 Service Update."
Out with the old
Using getServerUrl on it's own always had the potential to cause 'Access Denied' messages if the browser domain Url was different to the server Url stored in the CRM database. This was to do with cross domain access restrictions in IE. A work around was to use a method similar to Daniel Cai gives in his post on the subject - http://danielcai.blogspot.co.uk/2012/02/get-right-server-url-in-your-crm-client.html
In with the new
The SDK described the new getClientUrl as:
"Returns the base URL that was used to access the application."
The function nolonger blindly return the server Url in the database - but looks at the url that was used to access CRM so that cross domain access issues will be a thing of the past!
Read more in the SDK: