This is actually a really good way of marketing affiliate promotions... usually it's called "article marketing"... but you will also see that it's referred to as "bum marketing".
The idea is that you would find a good keyword (somewhat in demand, but also low in competition) and write a good article and submit it to an article directory (e.g. ezinearticles.com, associatedcontent.com, goarticles.com, etc). Your article will be listed faster in the search engines, because it's linked to a high page rank (PR) website.
Essentially, what is happening is that Google relies on high PR websites for content, so your article has a great chance of being listed much quicker than if you had posted the same article on your own website (unless your website has a PR of 6 or 7).
Some article directories require manual review... i.e. someone will read your article and make sure the content is of high quality. They will more than likely reject articles that are purely promotional... and ezinearticles.com does not allow that you list affiliate links in your author bio... but your author bio could include a link to your website, which would have an affiliate link.
If you are interested in article marketing/bum marketing, I highly recommend
http://www.bummarketingmethod.com by Travis Sago.
Hope this helps a little... let me know if you have any questions.
Sherif