Agreed...it's a total waste of time. You may as well copy and paste the content to your site as nothing will be unique anyway. Unless you change every post by 50%+ it won't be classified as unique content. Most people understand your content should be unique to have any value whatsoever. Google does ban for using copyright content too. Especially when you get reported here: http://www.google.com/dmca.html
I thinks it`s a percentage of the post that you copy. And autoblogging, I mean getting the RSS feed into your own webpage and nothing else. Its stupid and pointless to do it otherwise.