Actually, I enjoyed reading her cv, which I think is useful:
http://www.psychology.sdsu.edu/new-web/news/JeanTwenge.jpg
She's likely no boomer, having gotten her undergrad in 1993.
However, conclusions may be intentionally skewed to sell books (bearing in mind book sales to Gen X are probably lower than sales to the Oprah-book-club-reading Boomers) or please superiors (since she's working at San Diego State, and a UChicago/UMich grad, she probably has ambitions to grander things). She has a few studies that lead one to think perhaps her bent may be typical psychological babble, but I think she's done some interesting research. Nonetheless, if I bother at all with it, I'll read the book on the shelf instead of buying it.
What's funny is that she has on the SDSU site a q&a about this that will lead everyone here to realize what a psych major she is. Her theory is that Gen X was built to high self esteem and when Gen Xers don't meet their own expectations, they lash out against attackers. This is particularly funny, because anyone who disagrees with her conclusions from Gen X will be in her eyes a typical Gen Xer. So this whole thread would 'confirm' her theory.
Doesn't that sound like some of the circular logic other psychobabblers have thrown at us? We're slackers...so we're bitter...so we're cynical...so we're slackers...
Never could stand psych majors.