It would be nice to be able to search by class.

A simple change to app/views/hosts/index.html.erb seems to achieve this:

diff foreman/app/views/hosts/index.html.erb fore1/app/views/hosts/index.html.erb
20a21,22
>           <%= f.label :puppetclasses, "Class" %>
>           <%= f.collection_select :puppetclasses_id_equals, Puppetclass.all, :id, :name, :include_blank => true %>