Good news first, after a little struggle I have the user and login
engines working together with out any changes made. Yeah! (running
engines 1.0.5 and trunk from the user and login engines)
One thing I’ve noticed, if you have a method in say, the login
user_controller, and a method in the user user_controller, it seems
that the login user_controller method is called. For a quick example,
add an empty list method to the login user_controller and see what
happens.
Also, it appears engines don’t play well at all with edge rails. 
I keep getting stack-level to deep, so we’re stuck in a stupid look
somewhere. Here’s a quick section of the trace to give some hints…
/Users/nstuart/Development/rails/frails/vendor/plugins/user_engine/app/models/role.rb:32
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:237:in
load' ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:237:inload’
./public/…/config/…/vendor/plugins/engines/lib/dependencies_extensions.rb:73:in
require_or_load' ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:30:independ_on’
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:36:in
associate_with' ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:209:inrequire_association’
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:209:in
require_association' ./public/../config/../vendor/rails/activerecord/lib/active_record/reflection.rb:87:inrequire_class’
./public/…/config/…/vendor/rails/activerecord/lib/active_record/associations.rb:935:in
create_has_and_belongs_to_many_reflection' ./public/../config/../vendor/rails/activerecord/lib/active_record/associations.rb:609:inhas_and_belongs_to_many’
./public/…/config/…/vendor/plugins/user_engine/lib/user_engine/authorized_user.rb:47:in
included' ./public/../config/../vendor/plugins/user_engine/lib/user_engine/authorized_user.rb:46:inclass_eval’
./public/…/config/…/vendor/plugins/user_engine/lib/user_engine/authorized_user.rb:46:in
class_eval' ./public/../config/../vendor/plugins/user_engine/lib/user_engine/authorized_user.rb:46:inincluded’
/Users/nstuart/Development/rails/frails/vendor/plugins/user_engine/app/models/user.rb:30:in
include' /Users/nstuart/Development/rails/frails/vendor/plugins/user_engine/app/models/user.rb:30 ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:237:inload’
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:237:in
load' ./public/../config/../vendor/plugins/engines/lib/dependencies_extensions.rb:73:inrequire_or_load’
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:30:in
depend_on' ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:36:inassociate_with’
./public/…/config/…/vendor/rails/activerecord/lib/…/…/activesupport/lib/active_support/dependencies.rb:209:in
require_association' ./public/../config/../vendor/rails/activerecord/lib/../../activesupport/lib/active_support/dependencies.rb:209:inrequire_association’
./public/…/config/…/vendor/rails/activerecord/lib/active_record/reflection.rb:87:in
require_class' ./public/../config/../vendor/rails/activerecord/lib/active_record/associations.rb:935:increate_has_and_belongs_to_many_reflection’
./public/…/config/…/vendor/rails/activerecord/lib/active_record/associations.rb:609:in
`has_and_belongs_to_many’
/Users/nstuart/Development/rails/frails/vendor/plugins/user_engine/app/models/role.rb:32
…And so on and so forth.
I think thats it for now. Sure I’ll have some more comments later once
I actually start making my own engines. 
Keep up the good work guys!
-Nick
p.s. As always, yell if you need some more info for debugging purposes
or whatever.