Now, I'm not saying that television should be your childs babysitter but it depends on what you want to do and what channel you are letting them watch. Cbeebies, for example, is a lovely channel with no adverts (hence no requests for the latest doll/horse/Nintendo game) and excellent, age appropriate programmes that children from 0-5 will enjoy (and perhaps a bit beyond). Other channels such as Nick and Nick Jnr seem to have no educational value whatsoever, so they are very rarely on in this house.
My children enjoy television and whilst I could happily let it babble in the corner of the lounge for the entire day, they rarely watch it for more than about 20 minutes without wandering off and doing something else in another room. Yes, I am a mummy who does leave it on whilst I also get on with my day. I often see my girls wander past as they have heard a particular theme tune and have gone in to watch a programme. Favourites include Something Special (S has learned quite a few signs), Mr Maker, Num Tums and Mike the Knight. They also like In the Night Garden... (for which I think, as an adult, you need to be on some mind bending drugs to understand. Same goes for Telly Tubbies).
If we are in the house due to (a) bad weather or (b) things I have to do...like housework (yawn, dull), then the TV is on and the girls will happily watch what they like and leave what they don't. Does it bother me? Nope! They have picked up some amazing knowledge from the TV and it isn't all restricted to children's programmes.
S has enjoyed watching almost every David Attenborough documentary, a series about the planets, various medical programmes and even the occasional One Born Every Minute (I don't need to tell her where babies come from, but she will happily tell you if you ask). She loves programmes about animals (wild or domestic) and has a very inquisitive mind. Providing I judge the programme as suitable for her or educational to her, I see no issue with her watching it (of course I do view it first I hasten to add).
The girls enjoy films too and every few days will ask for a movie to be put on. Generally these are just fun such as Despicable Me, Flushed Away, Gnomeo & Juliet, etc. S can sometimes sit through an entire film but N, on the whole, manages about 15 minutes before she is off to play with the dolls house or look at books (she is book crazy - unfortunately this means tearing them up at times too).
Don't get me wrong, this is not a TV only household. I read to my girls, we paint, swim, colour, bake, dress up, make puzzles, build towers, go for walks, play in the garden, listen to music, etc, etc.
S can walk along happily geocaching for 3 hours or more so my girls certainly aren't 'couch potatoes'.
So, does the TV being on daily hurt? In my opinion, not in the slightest!