My 3.5 year old watches about an hour a day. It's not strictly monitored, but our TV isn't in our main area so he tends to self limit so that he can play in the main open plan part of the house. I'm not a huge TV person, but I think he enjoys the quiet chill out time that the TV affords. Additionally, the TV is a total life saver when I'm trying to sort out a younger sibling, cook dinner or get stuff done. TV in moderation is great, and having a child who will happily watch a bit of TV has also helped out when we've been on flights when he's happy to sit and watch way too many cartoons.
Regarding what programs, I think that's personal taste and dependent on what the child is into. Many age appropriate TV shows have got an element of learning in, and ABC kids gets my vote.
I think 2 hours of any screen time is plenty- that includes computer, ipad and tv.
I think that what they are watching should be restricted to age appropriate material too, and that any channels with ads be watched in the presence of someone who can help the child break them down and critically analyse them.