I have implemented what edebill suggested in his answer to this question.
If I point to the gem in the usual way, with it installed in my environment
gem 'activerecord_datawarehouse'
rake -T does not show my rake tasks, but if I point directly to the gem source code, like
gem 'activerecord_datawarehouse', :path => "/home/acras/code/activerecord_datawarehouse"
It shows and rake tasks work perfectly.
What could I be missing here? I did double checked and the installed gem is the same that I have in the source code.