[I also posted a portion of this on the original site but thought it might also be useful here.]
Being a Technical Evangelist for Adobe I frequently get questioned about our published statistics. My response is that you should always test YOUR user base before you make a decision about building on any technology. And in most cases when companies do their own testing the results are within one percent of our published numbers. This is true for enterprise's, SMBs, media companies, etc. But occasionally I hear about some demographic where the numbers are totally off. For instance, if your user base is still working on green screens then you will find lower Flash Player penetration numbers there.
I think Slashdot should publish their stats about their users. It would be interesting to see what the Flash Player penetration is like with this demographic - especially considering I sometimes see Flash banner ads on Slashdot.
-James (Adobe)