The island is crowded

Last night's excellent "Lost" episode showed us Michael's time in captivity with the "others". Apparantly there's quite a number of people on the island. It's fascinating on how a show' cast about people stranded on a island grows more and more each week... By the way, what is up with the creepy lady who leads the others? And what did Walt mean when he told Michael that they aren't who they say they are, they're pretending???? Why do I watch this much TV? Why?