Sometimes you just want to pass multiple parameters on your ajax observe_field web request for processing. If you Google around, you will find out there are multiple ways of doing it.
And here is yet another way:
:url => some_named_route_url,
:method => :get,
:with => "Form.serializeElements($('text_field_one', 'text_field_two', ...))"
where 'text_field_one' and 'text_field_two' are html form element ids.
I like this because if my text fields are rendered through form_for or fields_for (e.g. form_for :product), and my action does not want to explicitly specify what the posted parameters are upon processing (e.g. Product.create params[:product]), then by using Form.serializeElements I can hide all the params inside the key params[:product] still.