I have family and frienRAB who haven't read the books (nomatter how much I try to get them to read, they won't bother) but they enjoy and understand the film series. Sometimes I have to explain the names of a few objects, but that's about it really. The series has been lucky that they've had J.K on set to observe filming and have had the same screenwriter (with the exception of number 5). When DH comes out in cinemas, I guess we can truly tell if all the knots are tied in terms of the films' plot and details. But I have yet to come across a Potter film that doesn't make sense.
And this is why I say that fans should go into the cinema with an open mind, otherwise they are going to be let down. If they do not let the magnificent books cloud their vision of the films, then they'll enjoy them a lot more than they do now.
Anyway, nice to see some support for films five and six for a change. Usually, those are the ones that get bashed because of cuts/changes etc...But I have full faith in the filmmakers. They knew the end of book 7 when they were filming HBP, so I guess that they have tweaked the plot a bit for it to connect with the other films and for it to still make sense with the events of DH, while crafting it in a visual form for non-readers to understand as a whole. Adapting a book is not as easy as some people may think.