I've read quite a few books about writing, and I can't say that I like this particular book. However, I can't say that I don't recommend it; it had its moments of brilliance (usually involving quoting someone else), and some of what I didn't like about it probably needs to be attributed to the writing styles of the era (first published in 1938).
Just to get it over with, what I didn't like was how the book felt condescending, mostly based on the number of I-want-to-tell-you's and the I-am-trying-to-get-you-to's. In one chapter, she uses another writer's article and parenthetically inserts her comments; I would have preferred to make my own opinions before reading hers. And she refers to what she calls "Truthfulness"--Truth with a capital T scares me because it implies a singular truth, which is not something that we humans are privy to (much as some of us would like tho think otherwise). Attributing this capitalization feature to the era of the writing though, she could have had a very interesting conversation with Tim O'Brien about capturing truth through writing.
Also, Ueland seems to subscribe to the belief that anyone can be a writer--she would have made a fantastic middle school English teacher, I imagine--and though I don't agree (there are plenty of books published that should have ended up in the editors' pitch piles), I think it is important to encourage students who might otherwise never even try (really try) to write a good story and so I would recommend this book to any keepers of libraries and middle/high school English teachers.
All in all, I don't think that there's much she advises that books about writing haven't been advising ever since. Keep it simple, don't try to force your voice, etc. Ueland's gems, I think, lie in quoting Van Gogh (on page 20) regarding the capturing of moments and Chekhov (on page 126) regarding characterization through dialogue and the personality and voice of the writer. Also, there is a paragraph (on page 86) in which she describes beautiful writing: "It is impossible to cut it. I try to take out a sentence here or there, but cannot bring myself to do it. They are all too good and necessary and contribute too much."