I've mentioned Google's problem with 302 redirects possibly "hijacking" someone else's page in passing before, always meaning to do a longer article explaining the situation more. The new Page Hijack: The 302 Exploit, Redirects and Google up from Claus Schmidt looks to do an admirable job of explaining the situation, so check that out if you want to come up to speed.
The key thing is that the situation seems to really only impact you if someone does a redirect from a URL with a higher PageRank score than the target page. But that can be done, and the situation has long been a worry to some webmasters.
Now Slashdot has discovered it: Google 302 Exploit Knocks Sites Out. Perhaps that attention might finally prompt Google to solve the problem, where sadly ample discussion on search forums and at search conferences for ages hasn't.
The problem has been discussed on Webmaster World for almost a year in so many threads I can't even begin to point to the originating one. Dupe content checker - 302's - Page Jacking - Meta Refreshes from September 2004 is just one example. Your site is at risk from hijackers is more recent, having started at the end of February.
Our own Come on Google, Fix it !!! thread covers the same subject, outlinks to some key Webmaster World threads and has comments from GoogleGuy on the subject. He says -- as Google itself has told me before -- that they see it as more a minor threat than a reality hitting many sites.
In fact, that thread gained some infamy when GoogleGuy went further and offered an amnesty to anyone worried about spam concerns, if they'd forward example URLs of hijacking. The problem is that while many complain about hijacking, they are also hesitant to have their sites examined. But it can happen. I've seen it. Others have as well.
You might also check out our Let's Test Hijacking A Google Listing, Duplicate Content Penalty Timespan or 302 Redirect, Duplicate Content Penalty Timespan or 302 Redirect and Google Indexing 302 Source URLs Under the Targeted Site threads. Still want more? Kuro5hin Discover Google Hijacking - Bless 'em... lists some discussions at Threadwatch.
That post got kicked off over this write-up at Kuro5hin: Google and the Mysterious Case of the 1969 Pagejackers, also worth a read, and with a huge compilation of further Webmaster World threads at the bottom.