I am a 17 year old christian teenage girl who has lived her relationship life according to this book and has no regrets. I have healthy friendships with a lot of guys but--amazingly enough--not a single boyfriend. And my life has been just fine for it. Actually, my life has been great. The whole point of the book is that there is a season for everything: a season for investing in friendships, and a season for dating/courting for the purpose of marriage. This has worked just fine for all the people around me (most singles in my church don't practice dating either), and there has been no lack of wonderful marriages. I don't date, but that doesn't mean I've thrown away marriage. I'm just using my time to serve God instead of committing my heart to a boyfriend right now. (Which is the whole point of the book).
It is actually a fun book, and very easy to read. Josh is not condemning, but he does let people know that there are other options out there besides dating.