For what it's worth, I changed that setting last night after a dismal RPM for the day. Like you, I have very specific niche sites that need laser targeted ads.

So far today, my RPM is the highest it has even been. The same with the CTR. However, my CPC has remained steady.

Overall, I'm happy so far. I'll try and remember to report back sometime in the middle of the week. It could just be a coincidence.

I turned it off some time ago. Though earnings have ups and downs (yesterday's CPC was about half of what it's been recently), but on the whole, I noticed better results once I disabled them. My sites, too, are very niche-specific, so I don't want someone reading about a health issue to see an ad for black leather shoes they looked at recently.

The reality is Google is still going to display whatever they want. Sometimes you change a setting and you won't notice a result for weeks.

And how can you know? Search is so personalized. I just watched a video tonight that said Google is using 57 different parameters for search. Things like Geo Location, Screen Resolution, Time on Site... basically everything they track for you in Google Analytics can be used to deliver a personalize search result based on user preferences.

Personally I find it can be annoying. If I'm searching for Car Rentals for a Miami Vacation and I live in Los Angeles I do NOT want Los Angeles car rental results because I happen to be on a computer in Los Angeles.

I have played with these settings and I find it's best to let Google do the Personalized search. If someone comes to your site about gardening and they were just visiting a car site... they will see a few car ads... and that can still convert. But if they only see Garden ads... then who knows if it will convert better or not? I've done some testing on my own site network of blogs and overall it just seems to wash out.

Google wants the small publisher to know next to nothing. They even pulled the CPC from their External Keyword Tool.

So flip the coin and or test. But all things given I'd let Google do what Google wants to do.

FYI: I've been running Adsense since it first came out in 2003 so I have millions of Ad Impressions to draw my own personal bias' from... not that they are always right... but usually.

I think the personalized ads are funny, I research all kinds of niches on google and ALWAYS see ads for stuff I don't care about, but I know it is there because I was searching for it on google to see what sites are ranking for that keyword

Also if some ladies husband searches for truck tires, then when his wife goes to a site about make-up is she now seeing truck tire ads?

Some people say they have better luck setting it one way or the other. I haven't seen anything noticeably different either way. I do see some ads that are more local and they tend to be something I probably wouldn't visit.

Definitely have them turned on! They can account for 10-15% of your income. The ringtones and make money ads pay well.