CN, Nick, Disney, Toon Disney, and Boomerang all have cartoons with the afterschool period, some mixed with live action stuff, but it's nothing that hasn't been reran to death before arriving on the afternoon slot anyone.
A big point I don't know if anyone's mentioned it (forgive if it has) is repetition.
Back in the day, we only had TWO options of catching our favorite shows: Watching it when it was on, or taping it and watching it later (This wasn't an option for me, sadly, not until the mid 90's). Failing either of those, you had to wait until the show cycled back around to that ep, which could be months depending on how many episodes the series had under it's belt.
Back then, syndication only aired the shows once a day (twice if we were lucky. I clearly recall Gobots, and possibly Superfriends, getting before AND afterschool airings on the pre-FOX affiliate in the early 80's.)
Now, we get the same episodes of Spongebob, Lazlo, and Hannah Montana (And the rest of CN, Nick, and Disney's shows) crammed down our throats at every point of the day, every day. Plus with DVD, internet downloads, Itunes, and DVR's factored in, you couldn't miss your favorite show if you tried. There's no work in keeping up with your favorite show now.
Then, if you wanted to see your favorite show, you had to literally be there when it was on, which determined if a show was hot enough for the affiliates. Now, you can just flip your show on anytime of the day.
There will NEVER be another huge fad the likes of TMNT or Pokemon because of over airing and availibility.
That brings me to this phrase I've always believed in: "Always leave 'em wanting more". There is no such thing these days thanks to being able to see any episode of any show with the click of a button.