Hi,
You may also want to try if_attribute :user_id => is_not {
user.id }, if your feedbacks table has a user_id column. In authorization.rb (inside of declarative auth), there's a method called "validate?" in the Attribute class. I *think* this is where the code in question is evaluated. There's a case statement for :is_not, and you may try dropping a debugger or puts in there to see the value of attr_value and evaluated.
Hope that helps,
Jeremy