Guest blogging does work. you just need to find good blogs that accepts guest posts. just another way of building backlinks and promote your site on other blogs at the same time.
there is a downside to it also. i myself do guest blogging and found one of my post turning to nofollow few days later. blog owner published my article as dofollow but then changed to nofollow later. this will only benefit the blog owner but not the guest blogger. be careful whom you deal with