its a good way for getting back links its help us for increase you page ranking....

Now that it’s possible to make a website at relatively little cost, start-up companies as well as established companies have many competitors when selling their products and services on the internet.

With this vividness of the market and Search engines forcing their search results further down the page in favor of their paid results, it is becoming increasingly difficult for companies to be noticed on the internet without paying Search engines for the benefit.

Forum
Q & A
Social Media
Blogging
Bookmarking are very important techniques.

Guest blogging could be a great source to get good graffic in short time so you should add this method in your list and get benefits from it.

Well said, It is most impotant conspect of the SEO.