One of the main factors of search engine optimization involves having a number of direct, one-way links to your website from other websites and directories. However, this has created a number of debates regarding the acquisition of these links.
The main question involves whether or not all links are created equal. If someone links you to their site, is that the same as buying a link from another site? The truth is, while all links will make a difference, some links will make more of a difference than others.
As far as SEO is concerned, earned links are believed to have a greater value. This is true for viral advertising as well, since they are links that people have purposely placed on their websites of their own volition because they feel that your site has some value; whether that be information, entertainment, or a great product or service.
The placement of the link will also have an impact on the way that search engines will weigh the link to your site. Though an accumulation of links will generally overcome any issue of poor placement, when the number of links is only building, this will make a measurable difference.
Links that have been purchased will help you get off the ground with your credibility among search engines. However, this can be very expensive, and difficult to maintain.
The best thing to remember is that while all links do count, and every link will help your SEO efforts, it is the genuine, non-purchased links that will get you the glory in the end.