On my mac, for some reason the file associations got messed up, and the default app for pptx files is now Preview, which doesn't seem to work. I'm trying to make it open with Quick Look, but can't figure out how to do that. I've seen that you can use spacebar and all that, but how do you just make it open by default?
While QuickLook is a system feature and not ordinarily accessible as an application, you actually can do this.
/Applications/Automator.app and select to create a new application. Add a Run Shell Script action from the Library by double-clicking, and choose to pass input as arguments. Use the following script code:
qlmanage -p "$@" &
qlmanage is the command-line utility application for QuickLook.
-p causes it to create a preview (i.e. display the document),
"$@" means "all arguments passed to this script", which are files and folders, and the
& causes our new tool to quit immediately, since its job is finished once QuickLook is called.
Save as "Quick Look" anywhere you like, preferably an Applications folder.
Now you can drag&drop files and folders onto the application and this'll launch QuickLook. You can also choose to open files or all files of a file type permanently with your "QuickLook application", which will simply open a QuickLook window displaying these documents.
If you don't want to create the Applescript by yourself, there is a nice little droplet for this, Quick Look Droplet: http://www.macosxautomation.com/applescript/quickviewer/index.html
Then you can associate your file type with it, like Daniel Beck explained.