I asked for the hardcover special edition box set (with stickers!) for Christmas a couple of years ago. When I got it, I started rereading the first one, and vowed to finish all of them before I had to go back to school at the end of January. I finished five of them, and went back to school with a hole in my heart - I NEEDED to finish it. 

I spent every weekend reading as much as I could. When I got halfway through the seventh book, instead of attending my four hour night class, my illustration professor said "it's fine, just finish it! I feel your pain!" I sat in my friend's dorm room and raced through the last few hundred pages. All of my friends love HP and have wanted to tell me everything that happened so badly. They went out to play a board game while I finished it. 

I came out a half hour later and said "It's done." We discussed the book for a few hours, and ever since, it's been our topic of discussion on a daily basis. Obsessed, I don't know, but I know that we are gripped by the characters and the story. :p