While waiting for Filevault to encrypt my hard disk, I clicked the iCal and Address Book applications.
Apple has been known for its consistent user interfaces, so I have no clue what got into them designing the leather interfaces of those applications. Hey that might look good on the iPad, but Leather has nothing to do on my shiny alu-MacBook Pro. Here is a picture of iCal.
Since I am not the only one being upset here, someone already created a new (old?) theme. You can download it at MacNix.