If you've used any of the 37signals software products, you'll understand why the authors have an awful lot of credibility to write a book about running a small company.
ReWork sets out their vision of what has worked for them, getting from day one, to turning over millions of dollars, and having hundreds of thousands of customers.
The book is short, simple, and concentrates on the basics, rather than going into hundreds of pages of detail and case studies. This isn't, after all, an academic treatise needing lots of evidence... nor, however, is it an autobiography. Instead, it's a straightforward set of views about what they found works for them.
I would strongly recommend this book to anyone thinking of setting up their own business.
My only criticism of the book is that, while it has a wider scope than their first book - "Getting Real" - much of the material appears to be lifted directly. Getting Real was about running coding teams, this is about running the wider businesses. I'd NOT read Getting Real before - I ordered the two together, and read them back to back - this wasn't particularly worth doing. Read this one, and skip the older tome.