One of the greatest features of the Mac App Store is the ability to download the latest version of OS X Lion and then make a bootable image of it.
I upgraded from Snow Leopard to Lion the day it came out but then had to do a clean install a couple of months later.
Instead of using my out-of-date installer I downloaded the latest version of Lion and did a clean install. No waiting hours fro system updates because my install medium was old.
With newer machines (2011 MBA, Mini, maybe the iMac too?) you can even start the OS install straight from the boot loader. It basically net boots the Lion Recovery image and then proceeds with downloading/installing the OS. Pretty slick.
I upgraded from Snow Leopard to Lion the day it came out but then had to do a clean install a couple of months later.
Instead of using my out-of-date installer I downloaded the latest version of Lion and did a clean install. No waiting hours fro system updates because my install medium was old.