Though I do think that some peopleº treat it as more than a short hand - and like all stereotypes it can cause more harm than good when actually believed.
º I recently heard a barista talking passionately about "Freeing Cascadiaºº"
ººNot literally one of the 9 nations, but a related idea
Can't say I entirely disagree: the PNW does have a definite bent to its culture (I've lived in PNW^H^H^HCascadia for about a year now - loving it so far).
I found Garreau's other book "Edge City" to have more impact on my views in the long run, and I'd recommend it.
I thought it made a lot of sense. I mean, you can take anything too far, and any place has a spectrum of people in it. Even so, as the author said, events happen differently in different parts of the country, and the difference is something you can describe.
It's possible to quibble with how some of the cultural areas are delimited. I would've drawn the lines differently - I think the divisions in Colin Woodard's more recent "American Nations" are more accurate (although also imperfect). The main takeaway is that the USA is incredibly culturally diverse, which is why it's so difficult to get things done on the federal level and why it'd probably be better served by even less centralization in government policy.
I found this book valuable, but for me it was preaching to the choir - it's pretty compatible with my own politics, and meshes with my own experience living in each of California, New York, and Texas.