Seems more like an edge case. If you look at bugmenot, the system works beautifully, and I am still amazed at how well it works, and how long the logins work despite the system being a bit sneaky and breaching the T.O.S on sites where multiple accounts and account sharing are forbidden. I wouldn't propose the system if it was going to harm the web in some way, and I said before that we can standardize it so that webmasters can allow a skeleton key to be used. Sort of like try-before-you-buy mechanism. Most sites do not have the luxury of some anonymous-user function where we can login instantly and start seeing walled garden information