My forms are built-to-purpse, and use DLLs loaded into AutoCAD rather than an external EXE. In otherwords, if I need to manipulate a list of data, then the form has controls to facilitate that - a grid view and some buttons. Anything that calls a command, function, etc. makes use of the existing CUIx interface structure to simplify development, deployment, and maintenance.
I do have a couple of "directory" type external files, but those are either raw HTML or code-generated XML with an XSL transform to HTML.