This is a nasty way to get your Google ranking up! Copy content from your competitors sites and once you have a higher Google ranking than them Google will discard your competitor’s sites because of the duplicate rule.
This tactic suggests to me at least two major dangers – the first is that your competitors can copy your site, cloak it, and possibly knock your site out with Google’s duplicate content filter. I’m looking into this more, so don’t get all worried. I’m not sure how widespread or dangerous this could be.