Not convinced by AdwordsPro.Sarah's arguments at all. In my ad campaign I have keywords with QS "great" (8/10 to 10/10) that have VERY low CTRs (if any most days)and others ranked "poor" or "okay" that have relatively high CTRs (c. 2-3%). Currently my best performing keyword, i.e. highest CTR, only scores 5/10. (Also interesting to note that although Google suggests £1.25 minimum bid for 1st page exposure this word currently averages position 2.7 at a bid of just £0.15!)

I think there's still a lot of confusion out there about what constitutes "performance" and also how all the various parts of an Adwords campaign get assessed for quality. Every part of your campaign has a quality score - the word, the ad, the landing page, the campaign itself, the ad group... and content network QS is different from search network QS. A basic best practice for fixing quality scores is to take the words with bad scores out of an otherwise good group in order to attain the lowest CPC possible for the remaining keywords.

Also, CTR, while used in determining QS on a keyword, really has less to do with the word than it has to do with the ad. Any idiot can write an ad that will get clicked on - just promise people free money for clicking on it. They won't even remember what it was they were searching for in the first place.

Cant see why they would punish you for having keywords in your AdGroup that have little impressions. Doesnt make much sense.