I can assure you that at any size, the image on my system (Vista x64 + Thumbnail handler extensions for DDS, TGA, DXT, PCX, TIFF, LBM, ILBM, PGM, PBM, MP4, MKV, OGM etc. etc.) are always the same. Exactly as it shows in Preview, or PantShop Pro. (excluding re-sampling)
Windows Explorer creates thumbnails and icons based upon COM+ Explorer extensions, and they should not take any notice of EXIF information. Where EXIF information should be displayed is on the Details property page. This is handled by a different COM+ Explorer extension, but you often install them with Productivity suites like MS Office or Libra Office to get Author, Editor and such details.
I have property page extensions for MKV, OGM and MP4 (over and above those which come with the OS) to provide details of bandwidth, horizontal and vertical resolution and (where possible) frame rate etc.
Acrobat often installs a Thunbnail / Icon handler for PDF files... but I don't use Acrobat, and the fact that I don't want to wait for a folder full of PDFs to generate thumbnails plays a big part in that decision. (If's a nice feature, but when it is available, it really should be optional) I don't cache thumbnails either, because I didn't like the "Thumbs.db" files XP/2k3 created and I still don't like it's equivalent in >= Vista.
This article is interesting. http://blogs.23.nu/d.../antville-5751/