Interesting
While this has been mentioned before, naming an ActiveRecord association :target will cause infinite recursion. Especially lame if you are building an app for assassins or mobsters.
The tracker team upgraded to 2.2 and saw a big increase in the size of their mongrels, and much longer start-up times.
In an erector widget it appears that respond_to? checks arity. For example:
self.respond_to?("some_method") # => false
self.respond_to?("some_method", some_value) # => true