I only became aware that the Saturday morning cartoons were gone from all the networks two or three years ago. I turned on the TV one Saturday, and planned to re-live an old tradition, but there were none on any channel!
The one I miss most is the Bugs Bunny/Road Runner Hour, and the other Warner cartoons. They still run the Warner Bros cartoons on Cartoon Network, but it's still not the Bugs Bunny Road Runner Hour.
Another I miss being aired is the original Johnny Quest TV series (20 episodes). That one I had the good sense to get on DVD about 12 years ago.
I loved that on Saturdays from 6AM to 12noon, we as kids ruled all the networks. And often after 12 noon in the 70's, they ran adventure movies, and shows like the Tarzan TV series, plus Space 1999 and other shows. It was a great time to be a kid.