How impressions are counted When someone searches using Google Instant, ad impressions are counted in these situations: The user begins to type a query on Google and clicks anywhere on the page (a search result, an ad, a spell correction, a related search). The user chooses a particular query by clicking the Search button, pressing Enter, or selecting one of the predicted queries. The user stops typing, and the results are displayed for a minimum of three seconds. Source: http://adwords.google.com/support/aw/bin/answer.py?hl=en&answer=187309
I have not seen a massive increase across my accounts, this was my initial concern that the imp, ctr and qs would all change. I have seen a number of changes over the last month and think Google are still playing with this tool