I have a younger cousin who still watches cartoons, so I've seen a few of these. Johnny Test was awful, and most of the current Cartoon Network offerings are just too crude for my tastes. I don't even have a clue what Nickleodeon has for cartoons nowadays besides Spongebob, which, regardless of the hate it gets, is still a pretty good show IMHO, especially compared to what's out there (the entire MTV franchise is going downhill really fast, and has steadily been dying since Y2K, at least as far as I'm concerned).
The shows that really disturb me, though, are the live-action ones. Someone else mentioned Jessie, and I feel like it's a prime example. As far as I can see, it only teaches kids to be argumentative, snotty little brats. Imagine everyone in the world was Diamond Tiara- that's the way this show portrays things. And most of the others are either very similar to that premise or are unbelievably boring, a la Big Time Rush. I'm embarrassed to have to admit that I even typed the titles to some of this trash.
But, overall, I think if you search long and hard enough, there's still good stuff out there. I'm sure my judgement on the subject is majorly biased by the fact that I grew up in the late 90s, and wish that my little cousin were watching CatDog and Dexter's Lab like I did, rather than modern shows that I have no nostalgia for. Because, in reality, those shows were probably just as poor quality, I just didn't notice because I was 7.