There have been a lot of discussions in my current work place about the use of Flash 8. At present we produce a lot of Flash content both for the e-learning project I work in and for more traditional web based resources. The current standards suggest Flash 7 as the plugin of choice.
I decided to have a look at the Flash penetration for my own website. There are some guidelines published on the Macromedia website which put Flash 8 at the 50% mark.
http://www.macromedia.com/software/player_census/flashplayer/version_penetration.html
The graph below (click to open) shows the level of use of Flash 8 on visitors to this blog.

The penetration for level is 64.71%, which is broadly what i imagined.

The other interesting stat is the broadband spread, which was much greater than i imagined.