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Is this possible that having similar content (90% the same in some pages) is something bad even when they target different countries ? Yes, there was a Panda and EMD update around Sep 27 which could have affected your website traffic. Are they EMD? If not, it could be Panda - which focuses on low quality and duplicate content. Does google send some kind of notification if your site gets penalized ? No, unless there was a manual review of your website - in which case they would send you a notification via Google Webmaster Tools. Re-written all the text, in order to show completely different texts, would it help getting back the organic traffic ? Yup, that's how you recover from Panda (for the most part).

The number one goal is you want to come off as natural in your link building efforts after Panda, so I would suggest a mix between the two.  This will come off as "natural link building" which google likes to see.

Thanks to both of you, I was kind of worry for being penalized. Thanks.

Well put Gianluca, I always appreciate your input.

Having the same content, in the same language to target different countries would likely be considered duplicate content. Sounds good for users and search engines to me. Not sure I understand this question. There are a variety of ways you can set country targeting on a .com domain - contact info on the page, country setting in Google Webmaster Tools, etc.

Meta refresh is not a good idea. here is a bit more on it http://www.seomoz.org/learn-seo/redirection