A friend asked me this....and here's my answer -
I have not Harry Pottered, but I most likely will. It isn't that I'm deathly AGAINST Harry Potter, there's just soooo much excellent literature out there. I won't push Harry on the kids, but if there's an interest I won't keep them from it. If they've tackled C.S. Lewis' more adult fantasies (I'll see what I think of his space trilogy this winter) and J.R. Tolkeim's LOTR and maybe some Chesterton, I'll feel like they have a base for great literature with great themes and wonderful messages. Just because we all love steak won't keep me from letting my kids have hamburger.
I'm not too worried about one of my kids being fixated on Harry because I assign so much reading during school -- they only have so much time for "fun" reading. If a kid got stuck in a series I wasn't crazy about, I'd just assign more reading from books I wanted them to converse with.
This article from Memoria Press spoke to the same thing and stated it very well. - If I'm concerned about Harry with a particular child, I might make it a book study (read it together, analyze it, discuss it - writing essays would probably take the excitement out of it).
ETA : I found this article by Elizabeth Foss' son (I have her blog link on the left 'Real Learning') to be very interesting and much the way I expect my kids to react.