I keep CNBC on because I want to know if there is ever another terrorist attack in the USA, the USA attacks Iraq, or a surprise interest rate cut. I figure those are just about the only things that are going to suddenly move the market is a massive way. But like others have said, by the time you get the news on TV, the market will already have pounded you if its against you. They could be in a commercial break when it happens. The biggest move I know of during trading hours was the first surprise interest rate cut. If you go back to that day and look at the tickdata, you will see the NDX index rose by about 1% per minute for the first 5 minutes, then rose some more the rest of the day. I think the total move was 15% that day. So I use that as a gauge. If I was in a position, and the market suddenly went against me by close to 1% or more in a minute, I am out of there. Who cares what the news was that caused the move, you don't have time to get the news. It really doesn't matter, because its going to be bad news for you. Get out now before you lose more. That's the way I look at it.
You're forgeting the other half of the story... the index shed almost all of that gain within the next two days, if I remember right. I wasn't trading at that point but I was looking at the historical futures data a few weeks ago... it looked to me like move in the futures was 300-400 points in under an hour, it then fell 100 points, then shot up again, only to come back down a few days later.