This is one to look for in the future — sadly, as it is, no released/stable browsers support it.
Eventually though, seemless iFrames will be pretty cool, inheriting styles from their parent. Sounds great, and will come in handy on occasion.
I haven’t paged through the entire presentation below, but anyone see any security holes, or possible phishing issues with doing something like this? Maybe not, since you’d have to have access to the parent