This rumour existed for a while with BTopenworld and their dynamic IP allocation. But has proven to be incorrect, if you remain connected you will always have the same IP address, even if you disconnect and reconnect quickly you may still have the same address.
ADSL is not a replacement for a leased line, it carries no service guarantees at present, but for hobby/home web hosting it is perfect. With the USB service it is possible to host websites, if your ISP provides a dynamic IP address this can complicate matters but services like DynDNS will provide a work around.
This is incorrect. Home networking is allowed but it's not supported. If you phone support with a problem they will not answer your questions. See our Home Networking FAQ.