1 A good choice, in my opinion.  Deathly Hallows has a lot of action scenes in it, and those take up huge amounts of screen time.  Goblet of Fire, book four, also had a lot of action, and I thought the movie really suffered because there was so little time to do anything but action sequences.

On the other hand, I thought Order of the Phoenix, book five, made a good movie despite being such a long book.  A lot of that length is Harry being an angsty teenager, and the story is both shorter and more enjoyable without it.

2 I bought Goblet of Fire but have never watched it. So I didn't bother buying movie 5, and probably won't bother with any of the others.

3 I rather liked part 4 and thought they did a great job condensing one of the longer books into movie size. I will admit that the ending of the film was somewhat anti-climatic, but that's a case of something that simply worked a lot better on the page than it does onscreen. The 5th movie did a fantastic job cutting down on the repetitive whining that plagued the book. To be honest, I think the 7th book would be better off as a single movie, for a couple of reasons. First, the 7th book reminded me a lot of the 5th, in that there was a lot of repetition and whining for a good portion of the book. It doesn't really kick in until the last 300 pages or so, and I think the movie could benefit from cutting some of the initial stuff. Second, I'm not sure there's a natural place to split the story into two separate movies (though I could be wrong on that). At this point, I feel like WB is attempting to just wring out as much as they can from the (enormously successful) franchise, but perhaps I'm being overly cynical.

4 From the previews, they're playing with part 6 quite a bit to add more action.  I suspect that they'll take the first 2/3rd of Deathly Hallows, spice it up with more action and call that a movie, ending around the action at the Gringott's vault.  Then the final movie can focus purely on the return to Hogwarts and the final confrontations.  That would probably work as well or better than just truncating out a lot of the first half of the book, and of course lets them keep the franchise active for another movie.

5 Careful with potential spoilers, please... I for one have not yet read books 6 and 7...

Carry on.

6 In fact, let's not talk about the details at all. (Thread closed.)