Thank you GD for posting that, a good review! I will add a few things from my perspective:
1) Not all PSFs are created equal. GD and I had good experiences, but some PSFs really are not much more than glorified observerships where you don't get much responsibility. I don't have specific names for you.
2) Along those lines, the curriculum changes based on where you do it. GDs PSF had a lot more clinical path in it, it sounds like, than mine did. My PSF was in anatomic pathology, which here included some hemepath but no other parts of CP. That was fine with me, and I think I could have done elective time in CP fields if I chose though.
Definitely a good experience for me. I went into it wanting to gain the extra knowledge and see how pathologists did their job, not necessarily intent on pursuing it as a career. But after a few months I decided it was what I wanted to do.
Some people will say that if you know you definitely want to do pathology, you don't need to bother with the PSF because you have the interest in the field, etc. That may be true, since it no longer counts towards residency. It seemed to help me in regards to applying for residency. It definitely helped on interviews because I knew more than the average applicant about the field I was going into, and the right questions to ask, things to look at, etc. Plus, I could prove to my interviewers that I knew something about the field, already having done a year in it, and that I could do the work and be interested by it. IMHO, a 1 month clerkship in path during 4th year doesn't really tell you what it's like to be a pathologist.
What GD said about it preparing you for 3rd year is right on. I went into my surgery clerkship right after finishing a year where I spent 6-7 months dealing with frozen sections and surgical pathology, and another 3 months of autopsy. So my anatomy in many cases was superior to that of the residents, and the knowledge I had in surgical pathology proved to be quite a boon during both rounds and in the OR where occasionally they were asking me advice on what the pathologist wanted to see (in regards to margins, etc) on specimens. You gain an understanding of disease that you can't really get anywhere else. I didn't have to stuggle through things like cancer staging and tumor markers, margins of resection, etc ,because I had been immersed for a year.
In my PSF, I was basically given resident responsibilities. I took call, did solo autopsies, came in at 11pm to prepare a frozen section for the attending. Sounds like what is at UCLA, except for all the CP.
The negative I heard the most when I was telling people in my original class about my plans for the PSF was, "Why would you want to take another year to do med school?" It's strange, really, because at places like UMass where the tuition is not so high nearly 20% of the class ends up extending to a 5 year track so that they can travel, do exotic rotations, research, whatever. So they basically end up doing 20 months of rotations over 36 months instead of the usual 24. But for some reason my PSF which was 12 months with 3 weeks of vacation is an unreasonable extension? Crazy. I got more education that year than I did in any other one year of med school, plus I got paid (only a little bit).
For more info - you can go back and look through our archives here, many people have posted before. The archives are a wealth of information, if you can get past the 50,000 threads on the outlook for jobs and chances for gaining a residency for an FMG.
Basically, though, people match to great residency programs without doing PSFs. It's certainly not a requirement. If you meet the appropriate criteria (Interested in the field but not certain about career, fascinated by learning about this side of medicine, willing to put in an extra year), go for it. There are lots of non-pathologists who have done PSFs and they are better physicians for it. I worked with a few surgeons who had done it, as well as one OB-GYN and their grasp of things seemed more solid, and they had different perspectives on things.