SharePoint and Infopath forms ideally go hand-in-hand. There have been times when doing a POC questions are asked if we can do a “Leave Request requisition”. Sometimes the data needs to be populated using other dropdown boxes.
Digging though information – I ended up landing on the Infopath Team’s blog. They have a great article on how to design “Cascading Dropdowns in Browser Forms“. A great article and must read if you work extensively on Infopath