In October 2003, I blogged about how much Windows Vista—then codename "Longhorn"—lookd like Mac OS X Panther. Apple CEO Steve Jobs' Leopard demo was a déjà vu experience, where the new Mac OS looks lots like Windows Vista.
Microsoft gave the first real, public look at Windows XP's successor during the company's 2003 developer conference. All too familiar from Mac OS X: Translucent windows; resizing Windows (that maintained integrity and quality of playing or streaming video); live search lists; common address book; and many more features.
Four years later, it's Mac OS X that would appear to be the copier.