We just finished a CU1 deploy at a greenfield site (sole Exchange 2013 RTM).
Happy to report that once we figured out the prerequisites needed on Server 2012, running the AD prep steps, and then CU1 itself that our Exchange 2013 RTM to CU1 update was successful.
We are now getting some weirdness in the Event Logs such as service failure and restart attempts with (service already started) on MS Exchange RPC Client Access Service. Exchange Search Service seems to be crashing, and then we are getting MSExchangeFASTSearch exception errors.
While the above seems to have been introduced with CU1, the fact that OWA now performs a LOT better than before and MIME based PDF attachments via copiers are no longer killed has brought some happiness to our client! :)
Philip