I have been quite obsessed with Harry Potter and I have ordered my copy of book #5 already!!
As for the changes. I think for some it might be appropriate, considering that you have to think of it as what the majority is. Sad reality is that majority of people who will read one of JKRowling's books will NOT know how to understand the language found in HP.
Also, younger children who are being read HP might get lost in the words, still somewhat older children will be able to figure it out if they are reading the words and are able to understand the context of the passage and/or sentence.
Still, as for me I would LOVE to get a hold of the Brittish copies, I find the language very interesting and I love how they talk on the movies, very authentic to the characters that JKRowling created.
I cant wait for book #5!!!!