Delete Posts From Your Blog - DON'T

From Grizzly: Google does not look kindly on sites which delete posts.

From American Nanny: if I have a post that I want to delete, instead of deleting it, I change the content. I would imagine that you could even change the title and tags if you wanted without getting on Google's bad side, however, why lose the link juice. If you want to change a post, try to keep it on the same topic, using the same keywords.