MacOS make previews of every type of readable file (.doc, .pdf, .txt, .ppt) via pressing a key combination (APPLE+something). I'm talking about launching a new window, not a external program like OpenOffice.org to see the content. The previsualization ends when user stops pressing the keys.

I think that this could be ver useful for Ubuntu users, if you could open for reading every readable file type (.doc, .odt, .txt, .pdf, etc).

It would be useful for leafing text files without the needed of opening the required program. Thus, the viewer is faster than the complete program, so the user win some time.