Unlike with previous OS X upgrades, you can only download Lion from within the Mac App Store. There are no hard copy DVDs to purchase. You purchase Lion once and you can re-download it again for all your other Macs. While Lion doesn’t totally revamp the Snow Leopard operating system, it does contain over 250 new features – many of which make for improved use and navigation of the Finder system and other native applications.
Some of the most notable features include gesture navigation, which enables you to use your Mac multi-touch trackpad. You will also be able to view on your desktop all of the applications installed on your Mac, much like your iPhone. Applications can be grouped into sub-folders for better management purposes. Apple‘s Mail also gets a big overhaul.
Downloading and installing Lion requires that you’re currently running OS 10.6.8. The upgrade will replace the Snow Leopard system but retain all of your existing content. You should, of course, back up and/or clone your current internal hard drive before making the upgrade.
We will be covering in more detail the new features of Lion in the coming weeks.
Source : Mac OSX Lion