For those who have not seen this yet, Eric Lander of Search Engine Journal, has pointed out a major flaw in Google's Behavioral Targeting system in AdWords. He has made a video that shows what happens when you search for a particular keyword and the paid ads that correspond with that keyword carry over to your next search. Whether or not they have any relationship with each other! What does this mean for you? You risk having your ads being served up on irrelevant result pages, wasted money on poorly targeted visitors, the maximum cost per click associated with that ad can allow it to effectively dominate keyword markets that it doesn't necessarily belong in and lastly, your quality score takes a hit and click through rates decline. Is this something that you want to have to worry about when your paying for your ads to be shown to a targeted audience? To read more about this and to view Eric's video demonstrating this issue, check out his post "Google’s Behavioral Targeting Flaws Put Advertisers at Risk" at Search Engine Journal
This doesn't mean those advertisers are charged. Also, most likely if you switched search terms your not going to click on an ad from the past one since you've moved on. I'm sure google is well aware of this and probably doesn't charge for the clicks\impressions if made. Guess you never know. Should this be in the adwords sub-forum?