the end of an era

I admit it - I'm a geek. I just finished reading the entire Harry Potter book series. Again. My roommates have all seven books. I own all of the DVDs already available. I think I'm in denial that there won't be another book or movie coming out.
My fascination with the world of Harry Potter has been brief; I read the first book only one year ago, after I moved into my current place of residence. Yet I was instantly enthralled, and read the entire series in less than a month. I think it took less than two weeks the second time around.

After rereading the series, I'm left with some questions:

1) What happened to all four of Harry Potter's grandparents? They couldn't have been that old when Lily and James died; Harry's parents were only in their early 20s. Since Harry's paternal grandparents were purebloods, they must have been a wizard and a witch, yet they died in their 40s or 50s apparently?

2) What happened to Dolores Umbridge? One would hope that she met a tragic and bitter end.

3) What happened with the Dursleys, and the Grangers? Did they ever come out of hiding after Voldemort's demise? I would have loved to see Dudley's daughter or son on the platform at 9 3/4 in the final scene 19 years later.

4) Did they all repeat that year at Hogwarts? It seemed like a wasted year for the students who were there, and for people like Harry, Ron, Hermione, Luna, etc. and all the half-bloods and Muggles that weren't allowed to attend. And did they repair Hogwarts magically?

I wish these questions would have been explained. Perhaps, if the rumors are true, some of them will be included in the rumored pre- or sequel books J.K. Rowling has hinted at. I'm not sure anyone will be able to capture the magic (no pun intended) of the Harry Potter books ever again, but I sure enjoyed watching Harry and company grow up before our eyes in the books and in film.

Now I'll begin searching for the next great adventure in print. Or maybe I'll reread the series again... Readers, what books have you read that you enjoyed so much you lost all track of time reading, or couldn't wait for the next installment to be published?