Over the weekend it looks like we officially announced the penetration numbers for Flash Player 9 and right now we're at 90.3% for mature markets defined as US, Canada, UK, Germany, France, Japan. Over 90% penetration in 12 months is pretty impressive and this version of the Flash Player is very important for Adobe. It included a brand new virtual machine that includes a just-in-time compiler that was meant to put it closer to .NET or Java for performance. It also included support for Flex 2, which is a more developer-friendly way to build applications on top of Flash.
I've found that a lot of people won't move over to the newest version of Flash until ubiquity stands at 80%. Flex 2 seems to be getting a lot of healthy growth, but now that the base player has hit that 80% threshold, we may see more people start to adopt it. With some pretty significant "dot" releases, including the most recent beta for H.264 support, it's worthwhile to point to this post by Emmy Huang about how to calculate penetration rates for Flash. Adobe has a pretty good idea of how long it takes new versions to get rolled out, so this is a good guide.
via Flash Magazine