I have a horrible confession. Ds (2yrs 9mths) watches a horrendous amount of telly (well, horrendous to me). He watches about an hour at lunchtime (while I get lunch ready, and while I clear up - the latter part I tend to sit down with him while he finishes what he watches). An hour at dinnertime (same scenario) and about half an hour before bedtime (we both enjoy winding down to Little Bear on Nick Jr).
This pattern started when dh was working away from home, ds was very clingy and frankly it was the safer option to keep him away from under my feet while I cooked. We got a bit better once we moved, but now I'm pregnant and ds has dropped his daytime sleep the old pattern has returned. I imagine with a young sibling around that's not going to change in the near future
All that said, I'm not too worried about it (except when I read studies that stress 30 mins max or the world will cave in...) He seems to learn a lot out of it (Cbeebies & Nick Jr seem very very good in terms of appropriateness and education), will quite happily play at the same time as watching or jump up and join in. On nursery days, tbh he's too knackered to do anything else - who am I to deny him a good method of unwinding? He is aware that TV has "special" times, that it gets switched off.
Most importantly he has LOTS of other activities. We go out at least once each day (tumble tots, nursery, P&T group) and I try and do a short activity with him for the other half (drawing, reading, letters, etc). He helps me with chores. He has plenty of opportunity for free play which I give him attention during and sometimes join in. He is a conversant, bright, cheerful little boy. All my instincts (when I'm not on a "I'm a terrible mother" day) tell me that this kid is not hard done by!!
I personally don't think it's the amount of time sat in front of the telly that's the problem, it's the associated attitudes, whether there are other activities available, etc.
I enjoy the television, but I don't tend to watch a lot now. Yet when I was growing up the television was on lots. In fact, I don't have any memory of my parents having any other leisure activity outside the TV. My son sees me read, use the computer, watch TV, do crosswords, go for a walk, etc...
Everything in moderation, even moderation.