Snow Leopard Pre-Order Bounds into Amazon's Bestseller List started accepting pre-orders for Mac OS 10.6, or Snow Leopard last weekend, and the upcoming OS has shot to the top of the Software sales list. Two different incarnations are currently 1 and 2.

The $29 single-license upgrade is #1, and the $49 5-user family upgrade is #2. Sadly for Microsoft, it's Windows 7 Home Premium Upgrade is down at #13. However, Microsoft Office Home & Student 2007 is #3.  Additionally, Microsoft Office 2008 for Mac Home & Student Edition is at #4. The top five is rounded out by Norton 360.

At this time, there's been no official release date given by Apple, but certainly, there's some degree of confirmation in the listings. Both products show the following caveat in their listings:
Please note: Official release date has not been announced by Apple, though they have indicated this product will be released sometime in September.