I've been struggling with getting UI defaults to apply to interactive reports. The particular use-case is to apply those when only creating a report (not using the form/report wizard). There was one question about it on the forum back in Dec. 2012 that got no responses so I started poking around in the help and the UI myself. It turns out that UI defaults seem to be migrating to the "attribute dictionary" in Apex 4.2. In fact, there's a mechanism built into the UI defaults pages to migrate those to the attribute dictionary.
Once I discovered this I found that it was actually dead simple (like everything else Apex!) to apply these attributes. From any Apex page builder page select the Utilities > Attribute Dictionary option from the dropdown menus and voila! you're presented with a report of page items and/or report columns that are candidates for updates.
So for all of you fans of UI defaults out there (and if you're not one you might want to jump on this little bandwagon now) make sure you familiarize yourselves with the new attribute dictionary if you haven't already.