Intersango relies on myopenid.com for user identification. However, it has been reported in the past that myopenid ids can vanish for no reason. It has been discussed here for example:

http://meta.stackoverflow.com/questions/88451/myopenid-account-mysteriously-vanished

Most disturbing of all, once your account is deleted it can be recreated by another person, and they can log into all the sites that rely on your id.