Adobe Lightroom v4 allows you to EXPORT DNG as version 6.6, but Adobe DNG Codec is version 5.6 only! So obviously the DNG thumbnails FAIL to display in Windows Explorer on Windows 7, etc...
Obviously, Adobe needs to update their DNG Codec to version 6.6, so as to support Lightroom v4. When will that happen? We are all waiting.
labs.adobe.com/wiki/index.php/DNG_Codec (DNG Codec is v5.6).
Better yet, why doesn't Lightroom v4 just provide the appropriate DNG codec to be included for everyone using Lightroom v4 on Windows? So as to display DNG thumbnails without jumping through hoops?
In fact, how about a collection of "Camera Raw File Formats" to be supported for Lightroom, instead of buying additional support from www.fastpictureviewer.com that allow Windows Explorer to see them as Thumbnails? That would be very useful for ALL of us.