I completely disagree. I can sustain a high CTR and send people where ever I want. The reason you have to give the user a good experience is because if you don't, you don't profit.
User-experience is related directly to conversions. It has absolutely nothing to do with CTR. The only way it could hurt your CTR is if you use the same general ad on a thousand keywords and people recognize you ad as garbage based on the generic text. The classic examples are ebay ads. Everyone recognizes them and knows what ebay has to offer. If they recognize site.com because they have seen it before, chances are they know if it is what they are looking for. That is the only way that user-experience can effect CTR.
Also, you say you get %20 bookmarkers. If that is the case, why would the return through google? Why not the bookmark? I don't bookmark stuff really, I just search google. I only bookmark pages that aren't easy to remember.
So yeah, I do revisit sites via google searches instead of bookmarking, but that doesnt apply because i wouldnt search for something so specific that i didnt want to click in the first place. That means, you could be hurt by return visitors only by being beat by a better competitor site or on general keywords. But again, general keywords don't get searched over and over again by the same users. No one searches "buy tv" over and over again. If they do, chances are they already went to your site and didnt like your price. So in the end, it wasnt the user experience that hurt your CTR, but rather your prices and once that person buys a tv, he will never hurt your CTR again.
Finally, if you are advertising on keywords that are brands, and you arent that brand, of course the return visitors will hurt you because they tried you once and you werent what they wanted.
I cant think of any keyword that you should be advertising on that gets return visitors that you dont know for a fact want your site.
[edited by: Soze at 2:19 am (utc) on July 13, 2006]