I wouldn't say LSD has a message per se, because I would define a message as intentional communication, and intent requires an acting, conscious subject. I'm not saying LSD trips can't be meaningful; I'm saying that any meaning such a trip has is the result of the conscious subject interpreting the experience just as s/he interprets other experiences.
That said, there are certain elements of LSD trips that appear to be common to many different users, and some of these similarities lead many to the same general conclusions, although individual interpretations tend to vary quite a bit in the details. Many who have experienced an LSD trip agree that it challenges the conventional understanding of reality as an objective, rational external world that obeys knowable rules; however, there does not seem to be one consistent view within the psychadelic community regarding what new understanding of reality should be adopted to account for the experience. Individual theories range from talk about tapping into "true reality" to abandoning the notion of objective reality altogether in favour of a more subject-oriented understanding of existence.
Personally, I interpret the psychadelic experience as a radically subjective one that cannot be understood or defined in terms of external/objective forces and phenomena. Psychadelics break the normal subject-object relationship by allowing the subject (i.e., the user) to effective experience her own subjectivity. In other words, it allows us to break the mould of experiencing reality as an external 'thing' that we are interacting with and allows one to experience oneself directly. The content of the trip (visuals/distortions, bizarre thought patterns/epiphanies, 'divine moments of truth' and other difficult-to-explain experiences, etc.) comes not from an external reality, but from within one's own self. IME, this radical ontological departure from status quo reality is a wonderful tool in promoting critical thought in all areas of one's life; once the false assumptions that have previously informed one's actions and shaped one's world view have been shattered, one is free to apply the same sort of critical, analytic thinking that is used to 'fill in the gap' and thus integrate the psychadelic experience to other areas - social structures, religious doctrines, one's own psychology, etc.
Psychadelic experiences are wonderful, enigmatic and vary quite a bit from one another, so the above is far from the only way that they can enhance one's life, but 'breaking the ice' of blind acceptance of externally constructed norms and encouraging further critical thought is, IME, among the most common and most dramatic effects of psychadelic use.
Wow, this turned out to be a long post... Psychadelics + philosophy major = good times.
