What does Google (Matt Cutts) think about guest blogging and the links that are generated from doing it? This excellent video answers the question.
This is the bottom line. If you did not sweat in creating the guest blog post Google will typically not give you link juice for it. That’s the hard cold fact. Write a light weight blog post of about 250 words, post it on a variety of sites, and maybe even use article spinning software in an effort to create unique content for each site and you really will not be getting link benefits.
Create a well written, informative, insightful blog post for a site that supports your industry and yes Google does like this approach. It’s all about the time you take and the insight you provide. Do not do guest blogging just for links with minimal effort on your part Matt and Google pretty much say in this video that it is wasted effort.