I'll cover the price, the security upgrade, the cool new features, the size reduction and make a fun little video demonstrating some of the features in Snow Leopard.

$29 dollars. The low price is largely because Snow Leopard is more of an upgrade than a whole new OS. It offers only a few new flashy features that mac users have come to expect. Most of its added features are in unseen functionality such as Grand Central Dispatch, that most will never see or care about. Just knowing their computer runs faster is good enough. Examining these aspects Apple marketing said $29 bucks is a fair price. I agree, skip a few drinks this weekend and you have your new upgrade.

Security has always been a big aspect enthusiast place on Apple vs. Windows. Sadly even with this new upgrade, Snow Leopard is not as secure Windows 7. Windows 7 has some new security functionality, such as Address Space Layout Randomization (ASLR) and Data Execution Prevention (DEP). Elinor Mills wrote a great article on it here. The real question about Max OS X security: does Apple need to have the latest security practices incorporated into their OS? If their OS isn't being targeted, yet, why put a large costly focus on having the newest security practices when it doesn't reduce any potential threats on their OS. This is a small advantage Apple has by having 5% market share next to Windows world domination market share.
SIDE NOTE: This will most likely be changing with future generations, have you seen a college lecture hall these days, it looks like a glowing apple orchard.

Finally the upgrade has the potential to reduce the size of the OS's footprint on your hard drive up to half in some cases. Curiosity has me wondering how they did such dramatic size reductions while still adding functionality.