In my adventures with the new charting plugin search request view I discovered a nasty little bug yesterday.
If you are making an Ajax request and the result of that request is a redirect Opera 9 and 9.0.1 will not automatically follow the redirect and fill the result with the contents of the redirected request. Instead it will provide you with a response with an empty body and a response status of 302. All other tested browsers, firefox, safari, IE, will actually follow the redirect and the response will contain the results of the redirected request and a status of 200 (if all went well).
In the case of the charting plugin this behavior manifested itself by filling the lightbox popup we created with nothing (not the most informative error). The bug is fixed in Opera 9.0.2 but if you are ever on support and someone is telling you that your Ajax stuff is behaving very strangely just make sure of their environment.

Ajax bug in Opera 9 and 9.0.1, fixed in 9.0.2