you get very good (!) CTR if you skip BROAD and just use [EXACT] and "PHRASE" matching.
Very tight adgroups, and i mean VERY VERY tight, negative keywords on campaign level like "free, gratis, scam, rapidshare, torrent" etc..etc..
KW mentioned in AdText, strong call to action.
I disagree with the importance of a landing page, i think it weighs more than 10%, maybe 30%-40%
Lading page needs at least some content, articles, Contact Us, Privacy Policy and Easy navigation.
If it were "only" 10% as you say i could promote "acne cure" on a porn site...but i highly doubt i get 9/10 QS on a site which is NOT related to the ad whatsoever
However, overall account performance counts AT LEAST 25%.....as well as performance of domains, eg. i had domains slapped BAD recently again and i had to move many ads to new sites, instant GRAT QS while on the old domains i had POOR. SAME landing page and keywords, just a new domain can make a hell of a difference.