Keep in mind that the only version of 10.6 that was "legal" (according to the EULA) to virtualize was 10.6 *server*. I've never tried with VirtualBox, but perhaps it has a check built in for that?

Our Verdict Mac OS X 10.6 Snow Leopard Server is a remarkable piece of software, but it’s really at its best when it’s matched with clients also running Snow Leopard.

Jesus Vigo goes over the steps to create a bootable USB to install OS X 10.7-10.8 and OS X 10.5-10.6, as well as how to put multiple versions on the same USB.

Officially, the Mac Box Set is the only upgrade path for users of Intel Macs running Mac OS X 10.4 Tiger, but the regular Snow Leopard installation disc seems to work just fine.

But OS X 10.6, as it's officially known, is paws-down the best Mac OS yet, and it costs a dirt-cheap $30 for those who are already running Leopard.

In many ways, Mac OS X Lion Server (version 10.7; Mac App Store link) succeeds, but it’s hampered by UI annoyances and inconsistencies that will probably be fixed in future updates.

Apple has seeded Mac OS X 10.6 Snow Leopard Build 10A432 to developers tonight. The 10A432 build has been rumored to be the Golden Master build for Snow Leopard.

Apple has announced prices and deployment plans for its education and business customers installing Mac OS X and Mac OS X Server, with licenses starting at $29.99 in volume.