Zynga has decided to tweak a little bit the propery-based achievements after tweaking the properties themselves, and therefore there are three property-based achievements we can now earn in Mafia Wars:
Slum Lord, for owning a level 30 Tenement (became impossible to get a while ago)
Land Baron - for having all the properties in New York upgraded to level 25
Real Estate Tycoon - for upgrading all New York properties to level 100 or higher
Thanks to Ewoks for letting me know about this cool change!