Lots of people (me included) have been complaining that Flash (such as for viewing videos on Youtube.com) doesn't work. You go and install Flash again (as prompted) and when you go back to view the video it's like you haven't done anything -- no Flash.
Here's the fix:
Navigate to C:\Windows\System32\Macromed\Flash
Then right-click over both 'Flash9b.ocx' and 'FlashUtil9b.exe', and choose Properties.
In Properties choose the "Security" tab. Click on the "Everyone" account (or add it if it isn't there), and the button called "Edit" and then check the box called "Full Control", click "Apply" and do the same with your own Windows local account name.
Once you have done this for both files, run the FlashUtil9b.exe and it should install and update and tell you to restart. Do so and you should now find that YouTube and other sites that use Flash now work.