I have had Flash installed for sometime but it no longer works in Safari. At least not for me. Other accounts on this (shared) Mac can still use Flash in Safari. Furthermore, Flash still works for me in Firefox.
If I go to the About Flash Player web page in Firefox it tells me "You have version 10,3,183,10 installed". However, going to the same page in Safari shows me the missing plugin box instead. So I presume this is a Safari configuration issue, but I can't find anything related to Flash.
System Preferences > Flash Player tells me "Plug-in version 10.3.183.10 is installed."
I have uninstalled and re-installed the Flash software without making a difference.
My OS is Mac OS X 10.5.8 (9L30), the version of Safari is 5.0.6 (5533.22.3).
Obviously the workaround is to use FireFox when I want to do something which requires Flash, but Safari is my default browser on the Mac, and this is just a real pain in the neck.