Yes, I read it. Partly out of curiosity to see what all the hype was about, and partly out of professional interest to see what made this such a self-publishing success.
The main thing I learned was this. All that stuff they tell you about having to be a great writer and practice your skills and persevere and be original if you want to be successful? That's bullshit. This is mediocre at best. It's not truly appalling writing, but it's not in any way good. There are tens of thousands of much better writers publishing their stuff on Smashwords and the Kindle store. There are many people writing much better stuff in the exact same genre of "billionaire BDSM erotica". So what made 50 Shades so insanely popular?
What you need if you want to be a successful writer is first and foremost, luck. Luck can transform a mediocre book like 50 Shades into a major success (and pave the way for all your future books to rocket to the top of the best-seller lists). Or luck can doom a literary masterpiece to obscurity. Success has nothing to do with the quality of your work or the effort you put in. It's just a roll of the dice.
Frankly, it bored me. It's the modern equivalent of a Harold Robbins or Jackie Collins or The Red Shoe Diaries or 9½ Weeks: absurd romantic fantasy with some kink, aimed at bored middle-aged housewives and young women looking to be daring and guys looking for something a bit pervy that they could get away with. (And those were phenomenally successful too in their day, despite being mediocre.) Half of the appeal of those was because they were known to push the edge of what was acceptable in the mainstream, it was cool to say you'd read or seen them. You didn't have to like them - it was more about showing how sophisticated and open-minded you were.
To be honest, it wasn't as bad as I expected. It just doesn't deserve to be the poster child for self-publishing. It doesn't send the message that self-publishing is the way for great writers to be discovered. Instead, it tells us that no matter how poorly you write, you could, if you're lucky, be a success. That's why we have a flood of truly crappy books thrown into the e-book lottery by untalented writers hoping they've written the next 50 Shades. And the depressing thing is that one of them probably has.