They're especially prominent in "in fill" developments (small patches of remaining land that are developed in mature neighborhoods).

They're oversized monstrosities that grew up before the housing bubble burst. They're usually cheaply and quickly constructed and look hideous.

E.g. http://maps.google.c...0.004361&t=h&z=18

For a microcosm of the US housing bubble, enter "grist mill woods" for the address here and look around - http://icare.fairfax...aspx?mode=ADDRESS That's the neighborhood shown in the Google map.

HTH.

Cheers,
Scott.