Over on his blog Edward Ferron asks "
Does anyone still build MDIForms?" Well yeah, I do. The current project I'm working on has the concept of a searcher window. This window has fields for defining a search criteria at the top and a grid to show the results underneath. You fill in your criteria and hit the search button, the grid is then populated with the search results. From the results grid you can double click or right click and select edit to edit the item. This sort of metaphor cries out for an MDI form as many forms can be opened from the search results form.