When Mailinator came out, people simply couldn't get over the fact that there was no login - I mean, how can you have email that doesn't have a login and password? It was a very strong paradigm shift for some folks.
For Talkinator, this paradigm shift has so far been the shock of "all of a sudden" being in a live discussion in a Talkinator room. Again, they didn't sign in or realize it would happen. Its rather common for people to not believe its actually live (often they assume its some sort of advertisement).
It took awhile for people to get-it as far as how Mailinator works. Paradigm shifts come slow - but they're often a lot of fun.