i just noticed the other day that Google uses an iframe for its login box. if you go to the adsense homepage, for example, it seems like it's one complete page, but the login area is actually an iframe.
the only reason i noticed is because they had a temporary server error showing in that area of the page.
now, this is google we're talking about, so i realise that it is 100% secure, and there's nothing to worry about. but it just seems a bit unsecure to me.
when you visit that homepage, people will see a little padlock on their browser to show them its safe. and they will also see the https: bit at the start of the URL. so normally you'd think its fine. but i'm guessing that 99% of those users are just like me and wont realise that they are actually entering their login details into a completely different URL.
in this instance, it doesn't matter, because its google. but if a dodgy site did it, how would you know that you are logging into another URL? there is not a single thing in your browser to tell you.