"Content that is not available ANYWHERE is all thats important, and good sharp tageting with accurate careful seo brings a good 11 to 13 percent click thru as well. And I use one block, one tower per page and take notice of googles heat map, but not to the detriment of your visitors.
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Be genuine make sites for visitors with a passion, about things you understand and give valuable information and you will eventually do well, with any add company long after google has gone." Nitrous