Those Mac users who upgraded to the most secure version of Adobe's Flash player just before the Snow Leopard install will find that an older, insecure version of Flash is back in their system. The latest version of Flash should, once again, be installed.
It appears that the Snow Leopard installer was locked into Flash version 10.0.23.1. However security issues were found with that version, and Adobe recommends upgrading to the latest version, 10.0.32.18.
There is a page at Adobe.com that will reflect back your current version of Flash. After the Snow Leopard install, you'll see this:
What you want to see, after the latest version is installed, is this:
Here is the page to downloaded the latest version of Flash.
For years, Macintosh users who use only the Flash player from Adobe have had to pay attention to Adobe security announcements, visually check their version, and manually download and install the latest version. The reversion caused by the Snow Leopard install shows that nothing has changed with either company to make this process more automatic, reliable and attentive to Mac system security.