Suppose i have 20 pages, now these 20 pages have similar looking content, almost 90% same, with difference basically is of city or a country name only. Will this considered as negative or something that can force an action. What i experience is that these all pages did pretty well for starting 1-2 months, always on first page, but now from last 1 month or so there are nowhere. Infact many other pages are nowhere, so one more question is whether these particular pages can cause action on the whole site.
I find it interesting that a few days ago you were complaining that spam sites were outranking quality sites ( [webmasterworld.com...] ) and now you are asking why your pages with 90% identical content aren't performing well.
That is different topic altogether what i observe in a different niche. This is with respect to one of my other site that required some pages to have similar looking content with respect to various cities. All the pages were coming in serp's till 1 month back but now they are not there along many other pages of the site. So the question is whether these pages can affect the overall keyword ranking of the site.
I have a similar situation, but I found ways to make the pages different. It's a matter of percentages. If 10% of your pages are 90% similar, you might get away with it. If 70% of your pages are 90% similar, you're probably dead in the water.