I know a lot of titles were abolished after WWI, but it seems like there were plenty around during the WWII era (e.g. von Rundstedt, von Kleist). Was this a function of people born after the fall of the Kaiserreich being forced to drop it but people who already had it were allowed to keep it? Was there social pressure to drop it, either in the Weimar/Nazi periods or after WWII (i.e. People wanted to distance themselves from association with the old regimes)?
Nobility was abolished as a legal class in 1919. At that time, titles became surnames (differenced for gender). They haven't disappeared but some families have gone extinct in the male line. Many people today choose to simplify their names in everyday life (Facebook, etc) and omit the preposition.
Source: Article 109 of the Weimar constitution: http://alphahistory.com/weimarrepublic/weimar-constitution-1919/