Re: Client support, we've heard about it
Any substantial change of the UI will confuse the end users, no matter how intelligent or knowledgeable they are. It is the job the IT department to make sure end users understand the changes, and to walk the users through the changes if they don't.
When we migrated from Notes to Outlook we had loads of IT guys run around in red T shirts for this very reason. Some of the server guys even actually liked talking to humans for a bit :)