I've just used this book to help me in my travels round Cuba and while it's not perfect, it was invaluable. The potted histories and local insights are all as well written as you would expect from the Rough Guides.
The book's usefulness is, admittedly, limited by the rapidly changing nature of much of Cuba. Paladars (the privately run restaurants) open and close all the time, musicians spring up here and there and then vanish again apparently without warning. And such seems to be the way of things in Cuba at the moment - all part of the charm. You just have to go with the flow and sometimes you strike gold, other times you find that the gold has moved on.
This guide contains accurate maps (better than many tourist maps available in Cuba - one good reason to buy it) and fair assessments of the more stable attractions such as museums, hotels etc, and that's about as good as you can hope for in a rapidly changing country.
To my knowledge the Rough Guide is currently a more recent edition than offered by its main competitors which in my opinion is a big selling point, given the changing nature of Cuba. If you're going, I recommend it. Don't rely solely on local maps and guidebooks which aren't plentiful and also tend to be slanted to emphasise what the Cubans think we tourists want to see and what they want to show off.