Using Tiled 0.12.2 (same with tiled-2015-05-22) and qt4-mac 4.8.6: opening (and modifying) example-files works fine, but after creating a new map I was not able to import any tilesets or PNGs. Not even from the example-files. Tiled opens the import-dialog and adds a tab, but the tab is always empty.
The Tiled 0.12.2 release and the 2015-05-22 daily build are compiled against and ship with Qt 5.4.1. Your qt4-mac 4.8.6 is not used by Tiled unless you compile Tiled yourself against it.
Hmm, I can’t reproduce this issue. Are you selecting “Collection of Images” in the “New Tileset” dialog? That would result in an empty tab, because in this case Tiled expects you to add the images individually by pressing the little “+” button below the tileset view.
You’re welcome! It’s another thing to add to the list of things to make clear in the user manual, once I get around to actually writing it. I’ve started a documentation site a few days ago at http://doc.mapeditor.org.