Selected answers from the Dumb SEO Questions Facebook & G+ community.
gaurav goutam: what is guest blog posting . Is it useful for seo ?????
Mike Weeks: It is you posting as a guest on somebody elses blog with links back to your own content. Google likes links
Anna Johnson: It's when you write a blog post on someone else's blog. There are a lot of people out there using this as a way to link back to their own sites. Google is cracking down on spammy guest posting http://www.mattcutts.com/blog/guest-blogging/ so be careful if you are thinking of doing this as a link building tactic. You can still use guest posting to your advantage you just need to make sure you select high quality and relevant sites. Offer something of relevance and make it interesting and shareable! http://www.seoworks.com/01-seo-news-views/the-fear-arrogance-of-the-guest-blog-post/
Randy Wilson: ..and nobody says you must have a link back to your site when making a guest-post in another blog.
Kyle Brigham: I actually just wrote a post about this the other day. Hope it helps! ;http://www.serpicoseo.com/blog/2014/01/guest-blog-posting-for-links-google-says-nope/
Jai Prakash yadav: no dear ,according to Matt cuts guest blogging official declare a spamming activity
Kuldeep Singh: +gaurav goutam ; We have already done a debate about guest blogging earlier when Matts updated about it. I have also done an organic guide for guest blogging and the importance of it for SEOs. check out my blog post - ;www.tisindia.com/blog/5-reasons-guest-blogging-still-crucial-seo-strategy/
what is guest blog posting . Is it useful for seo ?????? 
