Well, advertisers and channels have clued into the marketing frenzy of kids, so there are so many "blocks" of cartoons now that saturdays have lost that spark. Cartoons before school, after school, before bed, etc. Personally I agree with Eric in that most of the stuff nowadays is crap... Not just "crap" because heck I watched a lot of crap that I can't rewatch now (Hanna-Barbara anyone?) but things that are SO blatantly into product marketing (Pokemon, Yu-Gi-O) or that are just unwatchable/borderline bad for kids. Things with too much violence (yes, I sound like a fuddy-duddy, but I don't remember a lot of people *really* dying in my cartoons. as happens nowadays...)
I watched my daughter's TV intake and make sure to avoid anything with just random violence, though it's getting harder and harder to do...
TIVO has been a godsend in that regard - I record shows she likes and are parent approved. She gets to watch them any time she wants (well, if she's been good and she hasn't exceeded her TV allowance for the day.) In effect any time can be "Saturday morning" for her, but I at least we have some say into what she's watching.
And occasionally we get to coincide our tastes, like watching Teen Titans together. (She is such a future goth chick - her favorite's Raven!) Even I know to draw the line at things like Justice League, where the violence is a little more intense at times (she's 6).
Cartoon creators are also pretty sly about including things to give the parents (who they know are watching) a chuckle - Planet of the Apes references on "Hi Hi Puffy Ami Yumi", etc. They know our generation (are probabaly *from* our generation) and throw us the occasional bone.
Adult Swim is, of course, right out!! But damn funny for me and my wife...
Take care,
Laszlo