Here's something I learned today, which might be interesting for other people working on mapping or on improving user experience for map editors.
I recently found that when I searched for Isla Vista Elementary School, its place name listing included "Ellwood" as the neighborhood, which is incorrect - the school is in the neighborhood of Isla Vista (as you can probably guess from the name), not in the nearby Ellwood neighborhood. I wanted to fix this, but I was confused about where this Ellwood place name was coming from - I couldn't find a tag on the school that mentioned Ellwood, and I couldn't find a boundary/border/area for Ellwood that included the school. Part of the weirdness to me is that Ellwood is in the city of Goleta, and Isla Vista is in unincorporated county land outside of Goleta.
Then I asked about this on #osm IRC, and a person explained that to figure out what's going on here, I could look up the school on Nominatim (which I hadn't heard of before other than seeing a mention of it in the search interface and didn't know what it was!), which said that Ellwood was a nearby node. Then #osm told me the next thing I needed to know: that Nominatim was probably using the Ellwood node as a guess for the neighborhood since it didn't have anything better, such as a closer node or an area.
Ah ha! So I put in a neighborhood node at the center of Isla Vista with the name "Isla Vista". Now if you search for Isla Vista Elementary School, the generated address includes "Isla Vista" in the place name listing. It now also includes "El Encanto Heights" though, since that's another nearby neighborhood node - which is incorrect as a place name for the school's area. So it looks like I'll need to figure out how to put in an area boundary for Isla Vista if I want this to be more reliably accurate.
(Update: OK, the school isn't showing El Encanto Heights anymore, but now it's showing "El Colegio Road, Isla Vista, Santa Barbara, Santa Barbara County" as if it's in the city of Santa Barbara, which isn't right either.)
Isla Vista is an unincorporated area (and census-designated place) that has its own identity but also a history of being accidentally assigned to nearby cities by people talking and writing about it (through ordinary confusion), so it's nice to help build a source of geographic information that provides accurate information about Isla Vista's relationship to nearby neighborhoods and cities.
Also, it might have helped reduce my confusion to see a tiny two-word explanation of Nominatim on the OSM search results page and a brief explanation on its homepage instead of having to click a small link to Documentation to get an overview of what "Nominatim" means. :) Now that I know what it means, I see that in its FAQ it has some information for "How was the address calculated?" and "How do I fix the address?"
Update on 13 April: I filed a suggestion for Nominatim to improve its site header and improved the advice for how to fix address problems, with the help of a person on the #osm-nominatim IRC channel. :)