Links should look like links. Contextual links should stand out form generic text. We are in the biz of sales, so, be a salesperson. Text links sell far better than a banner ad, we all know visitors don't bang banners like they used to. I get tons more hits off of text links then any images.
You can still be subtle with the text links, "visit the promotions page for more info" <--- with aff tag inserted works well for me. Deep linking to a specific page on a site is meat and potatoes. They may want more info but not ready to commit, this gives the visitor the info, along with your aff tag cookied so they will be under you when they sign up, even if not at that second.
Hidden links are those that are white on white or hidden behind images.
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"If you shoot for the stars and hit the moon, it's OK. But you've got to shoot for something. A lot of people don't even shoot." - Confucius