Squarefrog, who has put together what I believe to now be the definitive Holga resource site, has done a focus test to see if the generally cites distances for each focussing icon are correct.
He writes:
I decided to dispell some Holga focus myths and actually test the focus distance for the 3 people, and 7 people (group) settings. My camera was put on a tripod and the focus fixed in the middle of each setting. Then I moved the tripod back 2 ft after each picture. All pictures were taken using the cloudy setting with the aperture mod, so the aperture was about f/10…
See the results in a photo set on Flickr.