The difficulty in the book is the oceanic prose; sometimes, quite frankly, it's hard to follow the plot through the scrim of Proust's often labyrinthine sentences. But for me it was worth it. After making my way through the seven volumes I felt as if I had glimpsed an entire age, seen into a specific man's soul. It took me over a year of disciplined reading, and I actually plan on doing it again.
The very best book to help you get through the seven volumes is: Roger Shattuck's Proust's Way: A Field Guide to In Search of Lost Time. It is essential, and without it I might have given up any number of times.
Here's one of my favorite quotes from Proust: "We believe we can change things according to our wishes because that's the only happy solution we can see. We don't think of what usually happens and what is also a happy solution; things don't change, but by and by our wishes change."
I haven't read the book and don't know anything about it except what Mr. Avrech tells us in his post, but I couldn't resist noting a post about a book that took more a year to read with the help of a field guide, and was still deemed worth the effort. Besides, I love the Proust quote.