If you have an Intel Mac (especially the MacBook Pro) be careful when installing new Web browsers. If you do and it seems like you don't have the Flash plug-in installed, it's easy to install a non-working version of flash over a good one.
The problem manifests itself like this: you innocently install a new Web browser (like Flock or DeerPark) on your MacBook Pro and quickly realize that you can't see any sites that have flash embedded in them. So you click on the little missing plug-in icon and it takes you to the Flash 8 download page, which you install. The problem is that this is a non-Universal Binary version of Flash which overwrites the working version that came with your Intel Mac.
Installing Macromedia Studio 8 also inadvertently overwrites the UB Flash player that came with the computer and installed a PPC version. Intel Macs need the Universal Binary Flash Player and there are two ways to get it back:
1) Dan Benninghoff suggested on the Apple Discussion forums that you can install the original Flash plug-in that came on the Apple install DVD by using Pacifist (shareware), a program which allows you to extract individual files or folders from the Mac OS Install disc. Another, easier way to get Flash working again:
2) Adobe/Macromedia just posted a preview release of Flash Player 8 (184.108.40.206) that also solves the issue.