Using exact keyword anchor texts for links used to be a very popular SEO trick that would increase your chances of ranking in Google for particular keywords. With Google's algorithm changes over the past year, this will no longer help you rank. Now, Google just tracks this so they can determine who is creating artificial links using known SEO techniques and penalize these sites accordingly.
In order to avoid getting your site penalized, it is best to shoot for earning high quality links, surrounded by relevant content. The link itself should vary in anchor text. I now use either the site name or just the url as the anchor text for about 80% of my backlinks. As long as the link is there the content on the page matters much more than the anchor text.