I remember reading news reports saying that Michelle Trachtenberg was joining the cast and, being in Australia and a little bit behind the US, we invariably heard that she was going to be Buffy's sister, so I knew that it was coming...but, I was expecting her to be like a half-sister and for her to have some non-mystical reason for coming into the show. When Dawn and Buffy turned around and said 'Mum' and it didn't get explained for weeks, and giles and the scoobies seemed to know who she was, well, it was all very confusing. Dawn was pretty darn creepy at first.