Seems like periodically_call_remote is deprecated in Rails 3, any ideas how to achieve the same functionality?
periodically_call_remote
If you want to continue using prototype.js, so you can do what follows:
<%= content_for :js do %> new Ajax.PeriodicalUpdater("mydiv", "/controller/action", { frequency: 5, method: 'get' }) <% end %>
More about Ajax.PeriodicalUpdater here.