Yes, site rankings can be literally highjacked by your competitors by (1) stealing your content and (2) using a 302 redirect. How does it work? GoodSite.com ranks in the number three slot at Google. EvilSite.com comes along and copies the content directly from GoodSite.com. Then EvilSite.com puts a 302 redirect from EvilSite.com to GoodSite.com.
Many believe that Google looks at this as EvilSite.com as the new page for GoodSite.com. Why? (1) Same content and (2) the 302 redirect gives it a spin. So Google will go ahead and remove the GoodSite.com page from the listings with its duplicate content filter and replace the listing with EvilSite.com.
Now of course, you got the 302 redirect sending all the traffic from EvilSite.com to GoodSite.com, right? Well, not if they are only giving this 302 redirect to Google through IP Delivery. What this does is effectively allow searchers to go to EvilSite.com, because the 302 redirect will not redirect the actual users.
The bate and switch worked.
A huge thread on this topic is over at WebmasterWorld.
I would like to thank Max Chirkov for giving me the details for some of this entry.