Finally, the dialog section in the HIG has made some progress. Thank to Olaf who knows Qt Designer much better than I do, we found a way to create a clean dialog layout for KDE4. The trick is to use the same ratio of spacers on bottom of each group box. Read more in the guidelines!
We are planning to provide some video tutorials how to best use Designer - stay tuned. We'll also upload the ui files when we found a good location (the wiki allows only images).
I appreciate feedback on this, as well as on the other guidelines drafted on this page: "General" and "Modality". Please comment here or write a mail to ellen kde org.