Courtenay I absolutely love it, and am reading the series for the second time. Perhaps, being 74, I'm a bit too old fashioned, but I, personally, would rather not let anyone under 16 read the books.
Spring I agree with the other commenters on the first in this series. However, I would not classify all books in this series as YA suitable. Book 2 goes further than Book 1 in regards to sex/swingers. So, I'd take a peek at books later in the series to gauge your comfort level.
Patti There is a small amount of inappropriate language, some talk of adultery and a swingers lifestyle as well. No gratuitous sex. Ok for kids over 13 I would say, provided you allow the language.