I have been researching for a way to communicate across multiple different domains. User finger printing and third party seems to be the only way out here but fingerprinting will require computation and storage at the backend and isn't perfectly reliable. Third party cookies didn't work perfectly in Safari and Opera but this presentation has a hack that made it work perfectly.
I believe pretty much every modern browser except Firefox comes with 3rd-party cookies turned off anyways, and I don't expect many people chance that default.
Not exactly. It works without any settings on Chrome and FF. Works with IE if you add a proper P3P header and works on Safari/Opera with minor hacks.
I found the leet/lolcat verbiage to be a little excessive in this preso. It seemed to reach the point of annoyance when it referred to Douglas Crockford as "The Crock."
the simplest (unmentioned) solution that works in all browsers is to use flash with a crossdomain.xml as the bridge