There is almost nothing a competitor can do to harm your ranking or have your site removed from our index. Your rank and your inclusion are dependent on factors under your control as a webmaster, including content choices and site design."
Google has made a few changes to its filters in the past few months that contradicts this statement.
302 Redirects can have nasty consequences for your web site. It happened to one of our clients that had a link to their site from a major real estate directory.
Google began dropping hundreds of static HTML pages with original content. Google verified our problem, and removed the dupe content penalty within a few weeks. Now all of the pages are back in the index, and traffic is back to normal. The RE directory in question has stated that they are looking into the problem. In the meantime, we had them remove our links.
Oddly enough, we did not lose our top Google rankings for the primary keyword set even with the loss of pages. However, hundreds of top ranked secondary phrases (local residential communities, etc) were in the tank, and the client temporarily lost about 30% of their normal Google traffic.