I know all the language folks 'round here have been griping about the verbing of this word for years. I've just reached my own personal boiling point regarding a different aspect: 'Impact' is value-neutral! Really!
Dear Worcester Telegram & Gazette: Don't say "The city predicts an annual economic impact" of however many dollars. You seem to mean that the city is predicting an annual economic benefit, so just say that. An 'annual economic impact' could just as easily mean a deficit or charge!
Dear American Cancer Society: Don't say "You're only one person. But that's all it takes to impact the lives of millions." Your ad on the front page of today's "Sidekick" insert in the Boston Globe then goes on to talk about a firefighter/cancer survivor/Relay participant, but your attempt at an inspirational lead-in doesn't actually have anything to do with improving (or seeking to improve) lives. Terrorists "impact the lives of millions" around the world. Is that really what you wanted to make me think about? No! Just say 'improve'! Your avoidance of 'improve' makes me think you don't actually expect to have a positive effect on anyone but wanted a verb with more oomph than 'affect' ... again, I don't think you really meant to convey that!
That is all.