In many places, cities annex properties one by one, resulting in borders looking worse than ol’ Gerry’s salamander (example). These seem distracting and mostly useless, as well as being imprecise and out-of-date (there are multiple annexations per year). It’s rather hard to update, since one needs to find all the city ordinances annexing land, and map out the individual property lines.
I have two related questions to discuss:
*Should they be in the data, period?
*Should they be rendered by default?
For the first question, I don’t see the harm (except in making it harder to edit), as long as we know they might not be up-to-date, but they are one of the main non-“on the ground” features we include. More-normal boundaries are usually marked by signs, but that’s not generally true for this sort of boundary.
As for the second, I’d say that they should definitely at least be given less prominence, if not made entirely invisible. This would require a new field, since we’d still want to show more-normal boundaries, as well as a way to determine whether to apply this field.
The example you give is quite a mess! Being in the UK I don’t really understand the annexing you talk about, but why are the boundaries so fragmented? Is there just not one boundary round the whole lot?
IMHO I think the boundaries should be in, but not mapped the way this one’s done. As you say they are distracting.
As for less prominence, apart from the usual cry of “don’t map for the renderer!” it would seem to be beyond the power of us mere mortals to influence this. For example, Mapnik and Osmarender both show disused railway lines by default. What on earth for? They are long gone. If a path or cycle track follows one then map it as such, but there’s no need on the general maps.
Also IMHO, as the variety of data in the database grows, the more I think there is the need for a flexible front end along the lines of openstreetbrowser.org that will let people switch anything on or off on the display.
I’ll get off my soapbox now! 
Most U.S. states are split into counties, and all land is within one of those, but much of the land remains solely under county jurisdiction, not within any incorporated city or town. A city can annex a parcel of land by request of the property owner, or a larger area by vote of the residents. Cities usually have to be contiguous, but this can include thin strips along roadways, allowing them to annex far-out properties. Here’s a map of Orlando annexation by decade: http://www.ci.orlando.fl.us/gis/pdf/GeneralCityMaps/Annexations%20Map%2011x17%20General.pdf In some places you can see the individual parcels that were annexed or left out.
Ok, thanks NE2