TV - How much is TOO much

In our house the tv's is always on, I hate a quiet house. So M is so used to the tv being on that it doesnt bother her at all.

The only time she really sits and watches is when Mickey mouse is on in the mornings. I personally feel there is a lot of educational stuff on tv (we have dedicated baby channels) and your responsibility is just to controll what your child watch.

However I do promote playing outside and with toys more than watching tv.

What would you say would be the right amount of time that you should allow your child to watch TV? Would you change the time as they get older? And should babies be allowed to watch?

Heard a brilliant tip on the TV the other day from a stay-at-home-dad. He uses 30min TV time coupons as a reward for his children.