The Egyptian ambassador has explained that Mubarak has transferred all of his powers to his Vice-President but wants to remain as a figurehead President.
I certainly can see why the protesters are not satisfied with that action. The Vice-President is the former head of the secret police and was hand-picked by Mubarak. He certainly would have the power to retaliate against individual protesters, if the general protest dispersed. Or he might decide to simply ride it out without more provocative acts.
The protesters seem to be more in favor of the Army taking an active role in ruling during a transition to civilian control via elections. The risk there is that an Army Council may decide that it's in the public interest for continued military rule.
There's not a lot of good choices here but it's possible that the Egyptians can come up with a more creative solution. I certainly hope so.