You're right about thumbnails. After "playing" with embedded previews (horizontal, vertical, with and without metadata), I've picked CR2 file of which embedded jpg was already replaced (that's why I said newer cameras don't have them -this time original was used). That is, only one thumbnail exist inside CR2.
Sorry for confussion... but these things happen when messing with metadata, etc. :-)
Yes, the first time (no CanonVRD present) DPP looks into Exif:Orientation (as for "starting point" so to speak), but after CanonVRD is written, Exif:Orientation isn't used anymore -even if we change Exif:Orientation afterwars, DPP will keep previous orientation. I see nothing we don't agree on here :-)
I've implemented embedding option into GUI having in mind:
1. User would like to see (from preview) his final work (no matter what converter being used). For very first time he may use DPP (for example), later he can change his mind and embed image produced by ACR. Does now embedded image reflect DPP's settings? No.
2. Embedded preview is just one of developed images we can get from raw. As example, I don't use DPP's noise reduction for hi-ISO images. I export TIF (no noise reduction, no sharpening), then I use another software for further editing... and embed result back to CR2.
What I'm trying to say is: I'm changing preview, only to have some "default" developed preview (ready for 6x4" print, if needed). And that's what I ment by "everyday" use.
And as said, I'm aware, that my way of thinking, doesn't neccessary suit everybody needs. This is where you can help by finding different/better solutions and sharing them.
Your procedure (the way of thinking) seems to be ok. But (from my experience), one can never be 100% sure :-) Why don't you make a "package", so other could download it? This way, you would get feedback about usability and possible improvements (and bugs eventually).
Enjoy the weekend,
PS: If you do freeware, don't ask users what they want (believe me, you don't have enough time for that) -they will make their wishes anyway :-)