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IMO there is no fixed % or ratio when it comes to the use of synonyms. The idea is to have as much relevant content as possible whilst not coming out as being to spammy. It also depends on how much content you have on the page.

Interesting question there Mozzin, I think it depends on how you are tracking the urls. I think it will also come down to the number of affiliate urls that you have coming in and also whether they are followed or no followed.

We tried to change some of these affiliate urls to no-follow and saw a bit of change in rankings following one of the Google updates to do with links. (correlation does not mean causation).

As for using iframes maybe you can take a look at this post here on Moz,

http://www.seomoz.org/q/using-iframes-for-affiliate-ads

Most forums that still allow you to embed a link in your signature now have a minimum post count before you can put a link in your signature. Ultimately this ensures that you at least engage with other forum members and add value to the forum consequently before embedding the link.

wouldnt have put it better myself. Directory submissions are still worth the effort IMO as long as they are relevant and as KLLC put it , the directory is not built for seo purposes only.

IMO there is no fixed % or ratio when it comes to the use of synonyms. The idea is to have as much relevant content as possible whilst not coming out as being to spammy. It also depends on how much content you have on the page.