After 5 years of living on the fence I have started getting down and dirty with drupal code due mainly to this! Still banging my head with drupal api's and how the heck does php do x.. But it's a fun road.
PS: some of the modules you have referenced I thin it was awesome relations or something along those line in these articles has been abandoned... Any word on the 'street' what going to be happening in it's space?
Thanks for this article always a pleasure for some how to stuff for the ramp up. Maybe a flow up with Using entity API at some stage?