I've grown to hate that book.
As a teenager reading I Kissed Dating Goodbye, Joshua Harris didn't quite persuade me to give up what I thought was 'dating' altogether. His strong suggestion to couples for them to save even their first kiss for marriage (that was the way I read the book, anyway) didn't quite win me over, but it did cause me to save even that for quite a while.
Having said that...you find ways around these rules if you have the desire to.
But my standards made girls I went out with (N.Z. slang for 'dated') wondering if something was wrong with them..."what straight guy would turn THAT down...he's obviously not that into me" was what I'm sure went through their heads. And it caused me a lot of problems in my relationships.
Naturally, in my second relationship, I moved very quickly away from the perspective I got from Joshua Harris. Didn't seem realistic aye.
I have to take responsibility and not blame all of my relationship issues on JH, but I really don't appreciate the influence his writing has had on my life. Having said that, I still think he does have a few good insights in his books. Maybe worth a read, even, but take it with a large pinch of salt.