When I read The Art of Electronics, I already had a BSc, MSc and I was almost through my PhD in Physics. Even though I had taken many courses on electronics, specialised in electronics and done electronics design working for two companies, reading this book marked a before and after in my career. I read the book from cover to cover and learned how to design electronics whilst having fun.
I have also had the opportunity to put into practice what I learned by reading this book both as a hobby and at work. On many occasions I would think in disbelief "Holy cr*p this thing works!". This is because this book condensates over 30 years of electronics design expertise. As a result, my electronics design skills improved considerably.
You might wonder, where did I get the time to read such a big book? The answer is simple, I read it in the bus every day on my way to work. All that it takes is patience, and the time that you invest reading it will be highly rewarded.