Depends on the movie, as they get progressively more dark/scary/complex. Reading the books first is a must for my family, as the movies feel quite abridged and I want my kids to experience all of the surprises and details of the stories within their own imaginations first. Reading first has naturally spaced out our viewing of the movies, which I think is a good thing for age appropriateness. I started the series with my oldest child over Christmas break when he was in first grade, and we are midway through the final book now almost two years later (sniff). We watch each movie together after finishing the book, and I feel that so far he has been at a suitable age for each one. My voice will get a year off from the wizarding world before I start it all over again with my second, who starts first grade next year!
Yes, exactly!! Our kids were not allowed to watch the movies until they read the entire series, as I wanted them to experience the magic through their own imaginations, and without any outside influence from the movies, first. Which did naturally make it so they were a little older - about 8 - before they watched the movies, which was a good age for them.
My husband really wants to watch them with our 5-year old, but he hasn't had much interest in "real people movies" yet, so it's probably too early. I also like the idea of having him be old enough to read the books first!
I made my older kids wait to see the movies until after we read the books together. They were about 8 and 6 when we watched the 1st movie. It took a couple years to read through book 7 and see the movies, which was good because some of the later movies are dark/scary.