For the following error:
In file included from db.cpp:6:0:
db.h:14:20: fatal error: db_cxx.h: No such file or directory
#include <db_cxx.h>

I noticed that my system installed to /usr/local/BerkeleyDB.4.8/include/, not /usr/local/BerkeleyDB4.8/include/  (note the '.' in front of 4.8 ).

Super easy to overlook, so I thought I'd comment in case it helps someone else.