Yes, schrute has hit on the highlights in a nutshell. I'll write about UMN more in the UMN thread.
I interviewed for a fellowship at Mayo, so I can perhaps add my 2 cents. If I'm not mistaken, there are people from Mayo on this board so perhaps they can chip in, or correct me if I'm wrong.
Mayo has ties all over the Midwest, if not the rest of the country, which is key when it comes to looking for jobs. They get calls all the time from groups looking to hire.
They're not afraid to spend money to make money - I believe each consultant (attending) has their own secretary, which makes the place incredibly efficient. Everyone has their specific role. Doctors are addressed as "Dr. So-and-so" at all times. Scut is kept at a minimum, because of support staff doing everything they're supposed to do (I don't know who cuts frozens after-hours though). They have great PR (see
stickyshift's post on Mayo consultations). I think they have a service desk at the Rochester airport to assist patients. That's the kind of place it is.
You'll work hard - you won't be in the position of wishing you had worked harder. (I'm told of someone who went there for surg path fellowship, didn't bother studying for AP boards and passed.) You'll see tons of material. You'll be a superstar at frozen sections. I've never tried diagnosing prostate cancer on frozen till I interviewed at Mayo. It is a well-oiled machine - imagine an appendectomy, signed out within an hour of the specimen arriving in the gross room. Autopsies are done FS-style too.
The consultants work hard too. Apparently there is a reverse hierarchy at Mayo - the resident leaves first, followed by the fellow, followed by the consultant.
Oh, and you do see regular H&E material. On the "sink"/general surg path rotation, the second day consists of looking at the H&E confirmation slides on the frozen cases from the previous day. Also if I'm not mistaken, residents get elective months on the surg path subspecialty services where they see all kinds of consult material.
They have a bunch of fellowships. Surg path/subspec fellowships include general SP, GI/liver, pulmonary, cardiovascular, neuro.
http://www.mayo.edu/msgme/labmed-programs.html
I think they have dermpath, which for some reason is not listed. No GU/Gyn/H&N, unless those are unlisted as well.
They take education and their reputation very seriously - at the last USCAP I saw a fellowship director single-handedly carrying material to staff their booth for the fellowship fair. I almost couldn't believe the job wasn't being foisted on a secretary or resident.
If they're not tremendously competitive, it probably is because of location (mention Mayo and people immediately start talking about how cold it is and how they could never live there etc.).