although it might be a good idea, as it was mentioned already, to let your readers submit some. i'd say that it might be a good idea to only self-submit posts you're particularly proud of in order to help boost your readership to the point that others will submit your not-quite-best work on their own. imo, ofc.
People tend to have a natural negative reaction to blog promotions by the blog's author or employees. Generally, if people like your blog they will subscribe to it and read the posts without needed to get the "feed" via some sort of social news site. This is less true if your site is very high-volume and somewhat less targeted (ala TechCrunch), where people then tend to rely more on someone else to filter out and submit the really good stuff.
If every "loyal follower" with a blog posted all of their updates here, the value would probably become very diluted.