As if we did not know how a 35 mm film looks - Microsofts star designer team has decided that a piece of that old and obsolete stuff simply MUST be shown every time Windows 7 shows a video as thumbnail in Windows Explorer.
This old and obsolete film-frame steals over 30 percent of the available space. Of course one can make the thumbnails larger - thus showing far less videos at a time.

I have been looking for a replacement for the Windows 7 Explorer some time now - and found the UltraExplorer which does not show the dreaded 35 mm film frames and where you can set the thumbnail size to what you need.
Take a look at http://www.mustangpeak.net/ultraexplorer.html

Btw: The UltraExplorer also can show only all media files in a folder and filter all the irritating .sfk /0/1 files out.