What you probably don't realise (and I only know because I sometimes use other IQ sites as a guest), is that a guest has a permanent profile too. Each time I log onto another site, I can see my previously asked questions etc. Otherwise, it would be hard to find your answers when you returned as a guest. I even have some IQ points (1.5) on the French site for closing and evaluating a question!
I guess for this to work you need to have cookies enabled