I plan on buying a lot. I'm not going to buy anything that I think is ridiculous, but I do plan on buying some of the cooler, unique merchandise that really makes it feel like you visited the wizarding world. For one thing, my wand is a must have. Then butterbeer and some pumpkin juice, and then all of the other merchandise (at least one house crest/banner)... I'm saving over $100 dollars, that way, I can budget, and see what I really want.
On an unrelated note, Harry Potter and the Half Blood Prince is now on HBO, and my sis is watching. She hasn't finished the books yet, and she asked me if Snape was evil xD. I told her I wouldn't spoil it and now she's is mad rotfl...