I limit content, but don't really limit time, because most of the time the kids aren't really watching, it's just kind of on...they're off playing this or that, and if they see a show they like they'll stop for a few minutes. I only let them watch Playhouse disney in the mornings, and PBS kids or Noggin in the afternoons. I was letting them watch Boomerang, and they were watching SpongeBob every once in a while, but I didn't like things they were picking up from the shows, so we went back to just those 3 channels. Or a DVD we have, if they want - though we've had to recently limit content on those too as my younger picked up a few unkind phrases from supposedly 'kid friendly' movies....the 4 yo understands to not copy them, but the 2-yo doesn't get it yet.
SO some days, there's a lot of TV watching here, sometimes there's very little. They don't *need* TV, and it doesn't turn them into zombies - they're fine if it gets turned off, and they get involved in other stuff. It's just one of many things they do throughout the day.
I have friends whose kids do turn into the stereotypical zombies, i.e., just sitting there staring and sucked in - so they limit time...if I had kids like that, I would limit time too...but my kids aren't sucked in/zombie type kids, so I just limit content. I don't let them watch shows where the characters are rude, sarcastic, unkind, etc. It's all gentle, friendly, nonviolent, noncommercial, etc.