The system is really optimized: the installation is quick start-up time is shortened, the software is installed and open faster (even the "old" software), the Finder becomes ultra responsive. Snow Leopard is particularly pleasant to use.
Incidentally, Snow Leopard takes up less space on the hard drive without cheating (that is to say independently of the measuring file sizes in base 10). Although today we are no longer just Go near, it's nice on a laptop.
Ergonomics is still good. The graphical interface has received some adjustments to make it more homogeneous. Migration is performed in one click: all the settings are automatically imported and include a personalized system in minutes. And unlike Windows or Linux, OS 10.6 is operational immediately after installation, configured and protected, while remaining accessible to hacks advanced users.
With a complete rewrite of the system, it was feared many software incompatibilities. But finally, Apple has very well managed evolution. Few programs become incompatible, and personally I have no problems whatsoever with big software or with small freeware, recent or older software. That said, if one uses old "exotic" programs, it will be wise to consult an information site like snowleopard.wikidot.com/start or Macbidouille, or update site (MacUpdate, versiontracker).
Considering the price of the update, quality of performance, robustness and performance, it would be a shame not to Snow Leopard on Intel Mac. And bravo to Amazon.com for its promptness and speed of transmission.
EDIT: A mismatch was found to use: the Canon software to connect a camera does not work, and no update is coming correct this problem. Fortunately the Image Capture software provides with OS X does the same effectively. Remains a downside for those using Canon software to control the camera by remote control mode, this is impossible until an update is not available ...