The update fixes an issue with Leopard's Migration Assistant, wherein personal data, settings, and compatible applications would refuse to transfer from a Mac with Leopard installed to a Mac running Lion.
It's important to note that this patch is for Macs with OS X , not for your new Lion system; as such, to install, you'll need to be running Mac OS X 10.5.8. You can download the 4.98MB update over Software Update on your computer or via Apple's .