This is a pretty neat idea.
I'm not entirely sure how I'd make use of the iframes, but I'm already testing this out as a bookmark clustering tool, so I find the open all feature quite useful.
Right now, my main use case for the iframes is quickly checking for visual regressions across all the sites I manage.
Every morning I would go round to all my sites and check each one by one from a set of bookmarks, to make sure they were looking good and accurate. This way, I can do all my morning checks from one site.