I installed Vista SP1 last night and all appeared to be well, but when I tried to access YouTube this morning, the Flash video player wasn't working; instead, I got a dialog pop up complaining that it couldn't load a DLL.

The solution however was very simple; download the Flash uninstaller from the Adobe site here http://kb.adobe.com/selfservice/viewContent.do?externalId=tn_14157&sliceId=2. Once Flash has been uninstalled, go back to the Flash installation page and all should be well in a matter of minutes: http://www.adobe.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash.