I'm on vacation this week and that explains this chapter (Not sure about the other 25, tho :)

The reason Harry's not using his magic is simple: Dobby trauma. He's still convinced that if he uses magic, something's going to come and snap him on the ass about it. Also, he figures it's rude to do magic when no one else can. (a plot point I keep forgetting to address, thanks for reminding me.