Back before March 2005 Google page hijacking was a serious issue. It took Google some time to tackle the issue and it was less of an issue towards the end of April. But then it sprung up again in June 2007. Since then, I have not heard much about 302 or proxy hijacking in Google.
A new Google Webmaster Help thread has a new example of one webmaster being 302 hijacked. What makes this thread interesting is the conversation around helping both the webmaster and Google isolate the issue.
Googler, JohnMu, confirmed the issue, saying:
Thanks for posting about this issue. The team is busy on a solution to this issue, but it might be a few days before it is visible in all data-centers. Hang tight -- it'll hopefully be changed soon!
After about 24 hours or so, the issue was fixed by Google. I guess if this ever happens to you, you should probably head to the Google forums.
Forum discussion at Google Webmaster Help.