I glanced at it. The concept is interesting, and the author (a retired psychology professor) is right that tickling gets almost no serious study despite being really prominent in human society. He's also right about the reason for that, namely that the subject seems "silly" to people and isn't a good way to get funding or advance an academic career.
Unfortunately his study design... isn't great. First, why does he only survey women? Tickling doesn't only happen to women, and not only women are ticklish! He never seems to explain why it's women only, except to say that tickling is "mostly a boy-girl thing." Really? Also, as he admits, since women had to find the survey online and agree to do it, the people who responded must be much more focused on tickling than most. Many of the quotes from women in different parts of the world seem to make WAY too big a deal out of tickling in their lives and communities. It's hard to believe that most people think about it THAT much. He admits some of that, but he thinks the data is still usable. It seems so skewed, though, that I really doubt it's much use.
Maybe it'll inspire someone to take the risk to do a bigger and better study. It doesn't seem like it would be that hard to justify studying the role of tickling in social interactions as a psychology topic!