Sushi is a brand new quick previewer addon for Nautilus. Once installed, just select a file in your file browser or on the desktop and press the space bar to view a preview. Hit space again or escape or click the X to close the preview. Text files, pictures, and videos are supported.
It was featured in the GNOME 3.2 Release Notes and there's been some buzz about the parts of GNOME 3.2 that aren't yet in the Ubuntu repositories. This app won't be installed by default in Oneiric and doesn't appear to conflict with any other default apps. The app seems to work for us and the several who've tried it (scrolling and font colors aren't that great in Ubuntu but it's just a 0.2 release).
Brandon Snider has done the packaging and we've submitted it into the Debian GNOME experimental svn repository where it's gotten some further review. We're using nautilus-sushi for our package name so that it won't conflict with the sushi-irc suite which is already packaged as source package sushi.
http://library.gnome.org/misc/release-notes/3.2/
Please don't have identical source and binary package names that are for completely different packages.