On my collection using Unix shell commands and exiftool:

Sorted by focal length:

find . -name 'IMG_????.JPG' -exec exiftool -FocalLength  -p '$FocalLength' {} + | sort -n | uniq -c 

Sorted by frequency:

find . -name 'IMG_????.JPG' -exec exiftool -FocalLength  -p '$FocalLength' {} + | sort -n | uniq -c | sort -n 

In slo-mo:

• find . -name 'IMG_????.JPG: all matching files under current directory (you may have to change the pattern for other naming schemes). Using this kind of pattern avoids counting twice (JPG and CR2 for me).
• -exec exiftool -FocalLength -p '$FocalLength': extract focal length
• {} +: process as much as possible is one exiftool invocation
• | sort -n: sort numerically (so '90 mm' is before '100 mm')
• | uniq -c: replace consecutive equal occurrences by single line with count
• | sort -n: (optional) sort on count

Output:

    271 10.0 mm
      9 10.2 mm
      5 10.5 mm
      3 10.8 mm
     65 11.0 mm
     10 11.3 mm
      7 11.6 mm
      3 11.9 mm
     34 12.0 mm
      9 12.2 mm
      7 12.5 mm
      3 12.8 mm
     33 13.0 mm
[snip]
      3 33.0 mm
      1 33.3 mm
    215 34.0 mm
    653 35.0 mm
      6 36.0 mm
    119 37.0 mm
     75 38.0 mm
[snip]     
    192 58.0 mm
      5 60.0 mm
    187 63.0 mm
      7 65.0 mm
   1661 70.0 mm
     12 74.0 mm
     12 79.0 mm
      9 84.0 mm
     15 90.0 mm
     12 96.0 mm
    745 100.0 mm
     15 109.0 mm
     12 116.0 mm
    367 120.0 mm
     15 123.0 mm
[snip]
    191 251.0 mm
    247 273.0 mm
    194 297.0 mm
    185 323.0 mm
    181 352.0 mm
    686 400.0 mm
      1 417.0 mm
      1 454.0 mm
     12 495.0 mm
     32 560.0 mm

2'30" elapsed on 12000 pictures (Core [email protected], from SSD)

With a strong influence of my two macro prime lenses (35mm and 100mm), my 17-70mm often used as its longest, and my 120-400mm often used at either end, and the occasional 120-400mm on 1.4x extender.