Personally, I find that clause to be both strange and unfortunate. Google's generally a pretty open and lenient company, it seems, and unless I'm misinterpreting their terms here, it's specifically forbidding us from talking about our CTR. Given the disappointingly minimalist info on Google's site about click-thru payment amounts and such, it seems unfair for them to squelch discussion of this issue externally.
With that said (and, without disclosing my own site's CTR :D), let me humbly offer a few suggestions for improving CTR:
1) Make the area near and surrounding the AdWords box contrast highly with the AdWords background so the AdWords box will stand out.
2) Put the AdWords box towards the top of your page, if not at the very top.
3) Ensure the area surrounding the box is not crowded with text.
4) Make the rest of your page boring.
Okay, just kidding about #4 :D
Seriously, though, the issue of CTR is certainly a double-edged sword, isn't it?
I mean, as Webmasters... for most of us, our goal is to create compelling content on our sites to capture the interest and loyalty of our members (I'm not even gonna use the word sticky here; that's so 1999 :)).
But in order to maximize our AdSense profits, we're looking to, well, send away our visitors as quickly as possible. Indeed, that's one of the things that most concerns me about the target="_top" current unchangeable default of the AdWords box. I feel that the more successful I am with AdSense, the more I'm consciously driving my visitors away.
I WANT my visitors to find my content so engaging that they visit page after page on my site until they slump over at their keyboard from exhaustion. This particular (exaggerated) wish isn't about me making a killing financially... it's about making visitors feel welcome, interested, appreciated, catered to.
I apologize if I'm seemingly hijacking the original question of the thread here, but I think my question begs asking or at least considering (and I'll feel dumb if this was already recently discussed here on WW):
What is the optimum balance (for each one of us) between keeping our visitors and sending them off for profit?