My situation is probably so far outside the norm with regards to asking for letters of recommendation, but I figured that I would throw my two cents in anyway.
1 – I applied to a grad program in my final year as an undergrad (not all that unusual)
2 – I was 52 when I finally finished my undergrad (odd, but not completely unheard of)
3 – I am a full time employee of the school where I finished my undergrad, and applied to a grad program (free tuition, plus I was on campus anyway, which is why I went back to school)
4 – I waived my rights to see any letter of recommendation.
The program I applied to only allowed for 3 letters, but I ended up with 6 -
Letter #1 – This one came from an adjunct faculty member in the undergrad program, I had taken a single class with him. He is also a fulltime employee of the school and I also have a professional relationship with him (same department, but different group). He sent me a copy of the letter, when it was submitted.
Letter #2 – This came from the advisor of my undergrad capstone project. He was also a fulltime employee & part time faculty. We had no professional relationship, but we did share many outside interests. He also sent me a copy of the letter after submission.
Letter #3 – This one came from a fulltime faculty member, who offered to write a letter for me, after taking her class a year earlier. She did not send a copy of the letter.
There were also 3 unsolicited letters that came in after I filed my application.
One was from a faculty member from the department of my minor which was totally unrelated to my major or the program I was applying to. He was also the only professor that I had for more than one class in the 7 years it took to finish my BA. I had run into him on campus one day, and we talked for a bit and I mentioned that I was applying to a grad program. A few weeks later, he told me he sent a letter, but did not send a copy.
The second came from a professor who was currently teaching an online course that I was taking. He was on the review committee, was impressed with my work in class, and inserted a letter into my application, without my knowledge. I did not actually meet him until after I was accepted into the program. He gave me a copy of the letter when I finally met him in person.
The third was already in my departmental student file, and came from the former department chair. I had taken a course with him early on when I went back to school, and spoke to him often before he retired. He had asked me several times if I was planning on applying to the grad program, and apparently wrote letters for several students in advance.
FWIW I think the unsolicited letters probably had a more positive impact on my application than the ones that I had requested.