Harry's presence -- and influence -- does certainly seem to make a difference in the way the Slytherin first years behave and interact with each other (and with students from other Houses).

I am interested to see whether we are really seeing a different alignment among the Slytherin girls or whether Sally Anne appears to be emerging as girl-to-know because her player is more active in this early stretch of the game. (I don't have a sense of how meta-planned these posts are or whether players have a free reign to run within a general plot line for the game.)