I am a doctor (although currently in a very junior position), and my employer, the local public health care provider, is planning on making patient records public in the very near future. (Link in Swedish, use google translate) For this reason, I have given this a bit of thought. From the larger perspective, I am all for empowering patients to access their records. The main argument against it, as I see it, is that there is a certain group of patients, maybe 1-2 %, where this hypothetically might become a problem. These are the patients who come from a position where they already have established a mistrust of healthcare providers, often (but not always) because of real or perceived mistreatments. There is a tendency among these patients to interpret everything said and done during their dealings with health care professionals in the worst possible way, reinforcing their distrust of health care in general. Having these people access their medical records, with all the latin, medical lingo and outright physician slang therein, could, I imagine, further fuel a feeling that something is going on behind their backs, which I believe is what is often at heart of the problem. On the other hand, you could also argue that it would have the opposite effect, reinstating a feeling of control in these patients when they realize that their doctor didn't write such horrible things in the journal about them as they might have imagined.
As for being a game changer, as some other people has suggested, I personally think this will have little impact on the whole. Really, as a doctor, believe me: we don't habitually hide things from our patients, as some people seem to believe! The kind of people who would use the info from their records to surf the web to find alternative treatments for their diseases etc., know all the meaningful facts even today from just discussing with their doctor. Knowing exactly how high their hemoglobin count was two months ago, and what exact differential diagnoses their doctor considered and decided to document last week, is hardly going to change that -- they would already have asked the right questions. Furthermore, the people who are overly respectful of white coats, have language issues and so forth, who could be considered most in need of information empowerment, is probably those who will make the least use of this service.