My writing group will find this ironic considering I used this very trope in a recent script, but I really don't like when writers resort to using the tried-and-true expositional approach of the TV newscaster. It often feels lazy, like the writer couldn't think of a better way to introduce his world.
But the real problem is that most of these newscasts seem to have been written by writers who apparently have never watched the news in their life. If you want to see an example of this expositional trick employed correctly, watch the beginning of Tropic Thunder. After the long battle sequence, the film transitions into an Access Hollywood segment that drops a truckload of backstory on the audience. Why does it work? Because the scene in question sounds exactly like an Access Hollywood story, down to the bad puns and weak transitions. The writers absolutely nailed the tone and the cadence of that show and how it incorporates clips.
Bad newscast scenes feature things like remote reporters doing long live interviews for segments that would likely have been pre-taped and edited into soundbites on a real newscast. You'll also see things like two local news anchors discussing the issues of the day in a back-and-forth conversation more akin to Meet the Press than the 6pm affiliate news in Jersey.
There's also usually a lot of "As you know, Bob" type narration in these reports. True, the local news might recap some events for views unfamiliar with what happened, but it's unlikely they'd go into deep detail reminding the audience of the very specific circumstance two weeks ago that led to the mayor being arrested on charges of solicitation and drunk driving. In all likelihood, that would have been such a big local story that everyone in town would be aware of it. Thus, only a brief recap would be necessary.
So the next time you have the urge to write a newscast scene, don't. And if you're determined to ignore me, please at least spend a full week watching your local news so you get a flavor for how the pros do it.