First of all, thanks for the nice application that is XnView. But I like to make some suggestions about XnView Shell Extension.
1) Don't invert the thumbnail color whenever a mouse cursor goes over it. It's not visually attractive and, at least for me, drives me crazy. Maybe you can put an option do enable/disable the feature, or you can make a small border surround the thumbnail, and let only this border change the color when the mouse cursor goes over the thumbnail, that will be more nice in my opinion.
2) When we have a vertical picture with a big name, the thumbnail picture shows itself justified to the left over a big gray frame and under this thumbnail, we can watch, in a single line, the 'big name' plus the picture dimensions, the number of bits and the picture size in Kbytes.
I think you can include an option to break this single line, letting we choose to show the picture dimension, number of bits and size in a second line above the picture, and maybe you can add more options for the sequence of picture information, including the possibility to let the big names wrap in two lines or show in a single line but incompleted making possible for the gray frame aproximate the size of the thumbnail.
So the shell extension shows something like this:
[Thumb]
'Picture_with_extremely_very_big_name.jpg', 729x1024, 24 bpp, 245.7 KB
By all this I mean, include options for something like this:
[Thumb]
'Picture_with_extremely_very_
big_name.jpg'
729x1024, 24 bpp, 245.7 KB
or
[Thumbs]
'Picture_extremely_very_big...'
729x1024, 24 bpp, 245.7 KB
or even
[Thumbs]
729x1024, 24 bpp, 245.7 KB
'Picture_extremely_very_big...'
Well, thats all (I think)

Thanks and sorry for my extremely bad English.
Lukas