Western Forests published by National Audubon Society Nature Guides in 1994 is not a book I use heavily. I only picked it up quite recently though, so that might change. What has kept me away from it thus far is mainly that it contains things other than edible and poisonous plants. It actually runs the gauntlet from animals to trees to herbaceous plants all the way out to biomes. That makes it a great reference guide, but it isn't something I'm going to read through trying to commit each page to memory - there is just too much of it. It also uses photographs instead of detailed line drawings. That can be useful for adding more detailed color information to my mental models, but often I find it makes the plants slightly harder to positively identify.
All in all I find Western Forests to be a useful reference, but not a spectacular book.