Congratulations for SP1, it seems quite stable, scalable and ready for production.
But the whole thing looks a litte bit "loveless" with the new CU model. Many little and bigger things are not well tested:
RTM - Windows backup didn't work
CU1 - Problem with delegation sending
CU2 - Mailbox permission problem on move
CU3 - Outlook on XP didn't work properly
SP1 - OWA notification sounds broken
A lot of event log "spamming" entries (DatabaseDriveSpaceTrigger, MDP Ping timeouts) since early CUs, we can still send read-receipts in OWA only out of the preview window, no interim updates for bigger issues like the broken XP...
But using it for a year in production I must admit that the core system seems running well und stable, so I think the most new installations can start with 2013.