I spoke with one of the Engineers at Google working on this (I'm sorry, I forgot his name). He was telling me that a great deal of the security benefits of this

I spoke with one of the Engineers at Google working on this (I'm sorry, I forgot his name). He was telling me that a great deal of the security benefits of this can be achieved with iframes, but iframes require a second server round-trip. It is likely that this technology will be integrated with iGoogle and will result in a portal which loads in half the time.