Using observe_form
The documentation for observer_form is pretty sparse. It says:
Like observe_field, but operates on an entire form identified by the DOM ID form_id. options are the same as observe_field, except the default value of the :with option evaluates to the serialized (request string) value of the form.
It sounds to me like I should be able to do:
observe_form( 'search_form', :frequency => 1, :url => { :action => :search })
And have that work. Of course, if you do that, it doesn't submit any form values. With observe_field, you either need to specify :with=>'value' or use the :update flag. I've played around with a ton of options and never got anything to actually submit a full and complete form.
The solution is incredibly simple:
observe_form( 'search_form', :frequency => 1, :url => { :action => :search }, :submit => 'search_form')
That tells it to submit the form when a value is changed. That's all it took. I'm really glad to have found it, and can't believe it took so long.