Flash is one of those helper applications that many of us use on our computers to play videos and other multimedia content. however YouTube has switched over to a different technology, I would guess that only 20% of their videos still require flash.
I will repeat the advice that I’ve given my Mac user clients for the past couple years. if you really need flash, use it in the Google Chrome browser. Google keeps flash updated separately, therefore you don’t need to worry about updating it on your own.
if you use Firefox or Safari and have the flash plug-in, you will not be able to use it until Adobe updates it. that update may or may not be automatically pushed through to you. i’ll let you know when I hear any follow-ups on the situation.