Cascading Drop downs in InfoPath Web Forms made easy

To create user‐friendly web forms, cascading drop down list boxes is a must, but InfoPath Form Services doesn’t allow you to use them, like you can use them with InfoPath Client.
(Filter Data on DataConnections/DataSources are not allowed with InfoPath Web Forms)

This article explains how to use Cascading

http://www.silversandsassociates.com/HOW_TO_use_Cascading_Dropdown_ListBoxes_within_an_InfoPath_Web_Form.pdf

(Silversands Associates is very happy that already hundreds of companies used this article to get cascading dropdown list boxes into there web based InfoPath forms)