This is just a quick mockup I did a few months ago. I was trying Gloobus, which is nice. But I'm not a fan of having a quick preview being a popup. It's almost just as convenient to open the file itself.
I just thought I'd throw it up. It was quick, and doesn't look so great... but the idea is that previews should be integrated into the file browser. When you mouse over the file, the other icons would dim/become transparent - the preview should play in the background somewhere, while also displaying information in the statusbar.
PS - Dog in picture was adopted. Adopt another dog! [link]