Just used Ancestry on 3 day offer and for once really got some fantastic information but sometimes (1930 U.s. Census) it took lots of searching by first name, birthplaces to find relatives that I already knew about. Great-grandmother was Feld and couldn't find her brother, nephews, cousins, etc. Already had names, birthdate & places but they weren't in index. Tried Field but finally found some of them under names like Filt & Fred. My grandmother's uncle is still hiding there somewhere (I know where he and family were living but couldn't locate them in 1930).
One surprise however is my grandmother's cousin, wife and daughter appearing in census 3 times! Names, ages, etc. all match us except in one census his parents listed with wrong country of birth.