I saw all the episodes when they came out. I haven't seen them since. I would happily watch them. I even have some of the DVDs. My three year old gets run of the TV though and he's not a fan.
I actually loved Johnny the Homicidal Manic and Squee! more. They're comics/graphic novels/whatever done by the same guy who does Invader Zim. I'm more of a reader than TV watcher in general.