You should definitely code websites as if you don't have third-party cookies. It's always been our intent to ban them, and we're closing the loopholes as much as we can without breaking the web.
Yeah, we had to assume that because of the way iframes work in Safari. Its obviously great for privacy, but very frustrating from an application developer perspective. Too bad the interwebs are becoming more hostile and require these measures.
IMO the Webkit team would make developers' lives much easier if you more clearly articulated that intent; otherwise they have to guess the direction your team is heading and might build something in the short term that ends up breaking.
