Using the internet cache is fiddly and it only hold a certain amount and is deleted oldest stuff first. for youtube you are better off following Big_Johnno's advice and using firefox and downloadhelper extention to save them as a .FLV file then you can save them to cd or anywhere else you like. All you need is a FLV player to watch them.
oldbeefer, you might want to remember not all areas are able to get broadband. you have to be within 5klm's of the telephone exchange. some people do not have a choice and have to make do with dial up like it or not. Especially in country areas. And Not everyone can afford to get a satellite connection it is just too costly.
Allen