In the content network, one of my main keywords impressions shot up to 250,000. Any ideas on why impressions would spike and continue without any changes to the campaign? Thanks.
Possibly your advert has been added to a new site with a lot of traffic? I know that for one of my adverts a few months ago, the traffic increased ten-fold overnight, and I put it down to the advert being distributed more widely. Impressions don't cost anything, and if the clicks still convert well, it certainly isn't hurting you...
That can happen, if it's added to a busy site that's not very relevant to your advert. It's not costing you anything (as it doesn't affect the QS), so if you're happy with your cost per click and cost per conversion, then I'd probably not worry too much about it... If you start getting extra clicks that don't convert, it's a bit more of a problem.