ActiveRecord does not allow anyone to perform complex searches across multiple models easily. Currently in rails you are expected to know what the table name of the relationship you want to use is going to be
aliased too.

There are several problems with this:
* It's not intuitive to the developer about which table name to use
in the sql conditions (without reading ar docs clearly)
* It makes it difficult to generate advanced search forms, which can dynamically include or exclude queries

For more detail see:
http://groups.google.com/group/rubyonrails-core/browse_thread/thread/9ce088de0a3532c3/e5900a6047b41adb