Outbound Linking and SEO
Inbound links from external sites generally increase a websites Pagerank. However there is debate regarding outbound linking and its impact on Pagerank and actual website rankings in the SERPs. Basically there are different perspectives on the effect of these outbound links.
Outbound links do drain a web site’s Pagerank which is something Google looks at. There are ways to minimize the outbound link drain from the overall site by understanding Pagerank better. I am in the process of writing a post about Google’s Pagerank algorithms and Pagerank calculation. If you are intersted in Pagerank calculations you should read the post.
On the other hand if you link out to a relevant site then it makes your page more valuable to users and thus can help your rankings. Webmasters may link to your site and users may bookmark your site by hitting Cntrl-D (*wink*) and keep is as a place to come back to for other valuable information.
If you do choose to link out try and place the outbound link on the most relevant page and use the appropriate keywords in the link text which in turn can impact the search engine results for your site as well as the site you place an outbound link to.
As a rule of thumb if your outbound link is of value to the visitor I would go ahead and add it. Anything that typically enhances the visitor’s experience and increases the web site’s value to a visitor will result in better rankings for your web site in the long run.