My DD(10) does enjoy this if it's a book she's interested in BUT......I don't let her listen to the book INSTEAD of reading it, it's in addition to reading.
For example, she just finished reading the 4th Harry Potter (735 pages and worth 32 AR points!) This was a long, complex book (Reading level 6.8 according to AR). She started this book at the beginning of December and just finished it 1 week ago and she reads at least 1/2 hour every single night if not more. I got the book on tape from the library(12 tapes) and whenever we were in the car we would listen to the tapes and the whole family really enjoyed it....sometimes we got ahead of where she was at in the book and sometimes she got ahead of the tape. When we got down to the end....last 60 pages or so, she read along with the tape. She got 100% on the AR test by the way.
Books on tape are really fun to listen to but I don't think they should replace reading but enhance it.
Just got 4 magic treehouse books on tape for younger DS. He's already read 3 out of the 4 books and I thought he would enjoy this. He's hooked on this series (and he's only in 1st grade!)
So, try it, he may like it....if he has any interest in Harry Potter get those tapes, the guy who does the reading is just fabulous, lots of energy, you really feel like you are there.