I graduated from UCSD in 2008 and am now a resident there.
You are wise to consider the strength of clinical training. I think the clinical years are the true highlight of the UCSD curriculum.
The opportunities to work at six different hospitals is nice in that it exposes you to a diverse population of patients, but I don't think that's the main strength. Rather it is the UCSD culture of high standards, autonomy, and enthusiastic teaching faculty.
The 3rd year curriculum at UCSD is quite intense but at the end of it, most students function at the level of mid-year interns. Students are expected to function as independent providers for their patients to the greatest extent they are capable, and although residents and attendings are ultimately responsible, if you prove yourself your role in the formulation and execution of treatment plans can be central. When I was on my neurosurgery rotation I implanted a spinal cord stimulator from incision to closure with a little assistance from a resident as I felt I needed. In clinic, when I earned my preceptor's trust, my history and exam findings would dictate the plan, and the attending physician would only come in to greet the patient and confirm key findings. On anesthesia, all medical students deliver a general anesthetic from start to finish at the end of the rotation (I know of no other institution that does this).
Our attendings, almost universally, were involved in teaching by choice and enjoyed their role in our education. Residents play a key role in teaching at any medical school, and UCSD residents are generally very skilled and represent the top graduates of their medical schools.
UCSD's main hospital at Hillcrest is the former and current de facto county hospital and you will see the sickest of the sick and extraordinarily rare diseases. You will work hard, but when you become a resident, you should be confident in most situations that you have seen similar situations before and know what to do.
Let me know if you have any specific questions.
