While I think the iPad is a very personal device, my wife insists on using mine. That's OK, except that I get logged out of Facebook or other internet services. That's why a true multi-user design is needed. This one looks good.
Instead of showing a list, just give immediate access to different users right away. The design is limited to four people, but I can live with that. The concept of sharing the iPad simultaneously doesn't make much sense, however: