I do let my 3 year old watch tv. We have satellite and I let her watch nickelodeon. I know some think it is bad for kids to watch tv, but my daughter is learning a lot of good things from it. Just last week she learned to rhyme. Now everytime I turn around she is finding words that rhyme with each other.
I do have limits on what she watches, like I won't let her watch anything with bad language etc. Even some cartoons are starting to use words I don't approve of for a child.