You can take a test to see if you are an HSP
on her website.
Personally, like threadbare, I'm not too keen on the term 'highly sensitive' and would prefer something like 'highly reactive' or 'highly responsive'; partly because 'sensitive' can mean sensitive to the feelings of others (which HSPs aren't necessarily) and partly because it's just less girly.
It's this girliness that is my biggest problem with the book. There's a lot of talk about spirituality in it which I can't relate to at all. Also she has a tendency to make suggestions which strike me as being rediculously inapplicable to me and most (straight) HSP males e.g. HSPs are capable of looking at an arrangement of flowers and tell the mood of the person who arranged them.
I find it hard to love being an HSP as Aron suggests because it's viewed as such a bad thing for a bloke to be by this culture. To her credit, Aron does mention this a number of times in her book but doesn't offer any real solutions. Her main recommendation seems to be to have 3 years of Jungian analysis. I just haven't got the money for that and she doesn't offer any evidence that it would be beneficial only conjecture.
I don't want to sound like I'm negative about the book. I only mention these issues because I've sung its praises a number of times on here already. I would recommend anyone with SA at least checks out her website. It does give a much needed insight in to the upside of being this way. I'd still rather not be though.