Matt Cutts, in his recent video answered a question related to guest blogging, the question asked was like “I predict that in future Google will penalise guest blogging sites. Any insights on guest blogging as spam?”. While answering, Matt however cleared that there is no problems for organic, high quality guest blogging, but he raised some points for posting same content twice or more, spinning contents guest blogging as well as if you have adopted guest blogging as the only method of all your link building efforts.
Matt Cutts also published a video in past advising webmasters that Guest blogging should be done in moderation and should not be adopted as only single methods of link building, he again said that there should be diversification in your link profile so that it should look like natural, building guest blog links all the day is not going to do good for your website as Google have got technology to identify such low quality linking.
If you posting same price of contents twice or on more blogs, you should avoid this, this will be content duplication and not going to help, It is not called guest blogging, its like articles submissions publishing on number of websites. So you should think before guest posting same contents multiple times.
Spinning contents is another way of spam guest blogging, content spinning produce low quality contents and Google algorithm is enough smart to catch content spinning, spinned low quality contents are not going to help the readers, they are adding just low quality contents to the web. So avoid content spinning for guest blog posting.
Basically Matt said to avoid low quality guest blog postings with low quality contents.