I�m very leery of broadband limits. I find there are so many offers available that are economical and don�t have those restrictions that I believe limits to be rather old-hat. However, even with �unlimited� downloading, there are �fair use� provisions to prevent individuals from abusing the right.
Watching Youtube involves downloading. Saving is what you do once you�ve downloaded something�typically.
May I suggest that you look at the following site and see whether there are any deals that might appeal to you more than a restricted agreement:
http://www.broadbandwatchdog.co.uk
i wish you well
Fr Bill