Run Leopard on a virtual machine -- as long as it's on an Apple computer
You still need to buy a separate license for every Leopard Server installation. But in addition to installing Leopard Server on an Apple machine, you can install multiple copies of OS X 10.5 Server on a single machine. In other words, once VMWare and Parallels offer support for Leopard virtualization, you'll be all set.
This change does not apply to the desktop operating system. And Apple still strictly forbids installation of OS X on a non-Apple computer, which means there's no way to run Leopard on a PC without violating the terms of your license. Still, it's nice to see Apple crack the window a bit, even if they're not ready to open the door and let you run OS X, Linux, Windows all on the same box (unless you bought that box from Apple).