When at work my phone picks up the wifi of the coffee shop next door. That network is open but you have to accept a web certificate and put in a password on a login re-direct page every time you connect to the network.
This can be annoying when your phone auto-connects to the network but then doesn’t actually have access to the Internet (since wifi overrides edge and 3g connections for data).
What I discovered today though with 3.0 installed is that my phone had auto connected to the wifi network and I went to check my mail, which would normally result in it not loading and me having to either load safari and log in or turn off wifi and use edge, was that the iPhone realized it was connected to wifi but was not accessing the Internet, so it loaded a webpage overtop of mail (without kicking me out and opening safari) and allowed me to log in and then dismiss the page and continue with my mail.
Very streamlined, very much useful for coffeeshop networks.
The webpage acted much the same way an email overlay in safari would work allowing you to write an email while still surfing the web, only… Exactly the opposite.