Subliminal, it turns out, is an interesting study of the history of our relationship with the unconscious, but not much more than that. Mlodinow crams the book full of studies and experiments, and it can get a bit numbing after an extended reading session. But if read in small chunks over a long stretch of time, it can be a fascinating source of trivia. Mlodinow is a generous-enough host, and his anecdotes are well-told and obviously well-researched. But readers looking for information on how to access their own subconscious, or how to be more aware of unconscious decision-making, will come away sorely disappointed. (It's probably unfair to expect anything like that from Subliminal, but the subtitle—How Your Unconscious Mind Rules Your Behavior—does suggest a personal approach; I'd argue that something a bit more passive—The Secret History of the Unconscious Mind, say—would be more appropriate.) As far as pop science books go, it's a solid, if unsurprising, example of the genre.
Mlodinow reads from Subliminal tonight at Town Hall. If you're interested in the book, I urge you to go check the reading out.