Guys, if I write an article on my blog then submit that article to 100s of article directory. Will google penalize me for duplicate content?
Don't do it mate. I have seen a site I sold a while back drop almost all its pages from Google because I submitted all of the articles that were on the site to article submission sites back when duplicate content wasn't really an issue. It will extend your time in sandbox if you're in it for various competative keywords and you likely won't ever come out unless the content on your site is unique in most part. Create different or re-written content to submit to article directories by all means, but I wouldn't submit any content that is on your site to article directories nor more then you should poke yourself in the eye with a rusty nail. It will harm you. Pete
Modifying the article you submit from your original is a great idea. You won't be "penalized", per se, but your site may not show up at all because of duplicate content depending on which site was indexed first. Google simply omits the duplicate content.
I agree, but what if the site you submit to has a higher rating than your own, by the SE, whose content will be omitted?