Apple just released the 10.7.2 update to Mac OS X Lion, available now through Software Update. In addition to the usual bug fixes and improvements OS X updates provide, this version brings iCloud support.
It's basically the MobileMe you once had to pay for, but free, which is great if you just upgraded to iOS 5. It also adds a Find My Mac feature should your Mac end up lost or stolen. This feature works much like it does on iOS, letting you check your Mac's location online through the iCloud web site.
Apple issues Mac OS X 10.7.2 update with iCloud support [Apple Insider]