As the $US exchange rate is currently very weak, many Canadian AdWords Advertisers chose to switch to a $US AdWords Account, informs a forum in Webmaster World.
"I smoothly moved all my campaigns to a new account and paused the old ones, as we know they will not simply change the currency for you."
Sadly, you have to pause the old account while your new one is running. Due to this functionality, the advertiser saw that all his new keywords quality score was set to "poor," while it previously was "OK."
The problem and its solution is clearly mentioned in the following:
"Unfortunately, you're being affected by the account quality score, which takes into account historical data and your spend. We actually encountered the opposite where we launched a new client account under a new Adwords account and we couldn't get anything to show. Google blamed it on our account quality score, but they were otherwise unhelpful and cryptic. Finally, we sacrificed an old account, moved everything over, and our account quality problems were erased instantaneously. I would recommend running only your very best campaigns in terms of CTR on the new account. Run the rest of the campaigns on the old account. After you spend enough money and achieve a high enough CTR, you'll be in good shape to start unpausing the other campaigns."
Google's stance is that, "When converting currencies, we receive a daily feed from Citibank and use the average of the buy and sell prices to determine the exchange rate. Because this calculation is so granular, there is no advantage to bidding in one currency rather than another."