Posting a quick tip that I shared on the OpenSocial-Japan mailing list.

OpenSocial apps (gadgets) are displayed inside an iframe, and the query part of the URL in the iframe tag's src attribute actually contains the URL of the XML source code. With this bookmarklet, you can open the source code with just one click.

[Open Orkut Gadget XML](javascript:var%20inner_doc%20=%20document.getElementsByTagName('iframe')[0].contentDocument;var%20iframes%20=%20inner_doc.getElementsByTagName('iframe');var%20src%20=%20iframes[0].src.replace(/^.??url=(.?)&.*$/i,%20"$1");window.open(decodeURIComponent(src));undefined;)

↑ Save the above link as a bookmarklet and click it while viewing an Orkut app; the source code page will open in a new window. (If multiple apps are displayed, it will open the source code for the top one.)

*Note: I have only tested this in Firefox, so please let me know if it doesn't work.