I've read all of them only once. I got into some other series and haven't been able to get back to rereading them again. Also, to make it clear, the other series is not Twilight, I'd rather die. LMAO!
As a whole, I've probably read through the entire series at least 20 times.
When it comes to the different books, there are some I prefer more than others. I've re-read the Goblet of Fire and Half Blood Prince about two and half dozen times, with the Deathly Hallows coming in at a close second although I tend to skip over the ending.
I really don't like the fifth one all that much. I've probably only read it five or six times. I'm not too fond of the third one either.
The other two are a kind of normal number, like ten or eleven.
I'm on the last one. But I'm also reading the 4th one. I have not read the first one. I started reading the 6th after watching the 5th in cinemas. I found it more difficult to read the children hard cover books than the adult pocket version.
I think the first book looks really easy to read, since it's only 350 pages(not so many either). Well, I loved the 6th one and It was really pity for the movie with Snape. He was so little in it, but that's of the point here.
I'd say 6 times. 7th is still running, I'm on 4th book right now. But if I keep going like this, I'll have to buy new copies, they are so weather beaten. You know, I keep dragging them to the beach or onto the ship and everywhere when we go on holiday.