I started using iCloud for iWorks now that it is fully integrated with Mountain Lion (I'm using 10.8.2) and iOS 6 (Using 6.0). It seems that Apple wants you use the application to access the document. That is - if you want to open a keynote document - you open keynote. Apple have been moving that way for a while (Apps control documents). I did find some tips on getting to your documents in Finder.
Access all your iCloud files from the Finder sidebar - Mac OS X Hints
Basically your documents are in ~/Library/Mobile\ Documents which you can get to in Finder by going to the Go pulldown and holding down alt/option -> Library should show up as a choice.

Finder -> View -> Path Bar
I also found the documents in the "All My Files" sidebar item. You can open iCloud from the path bar - but it actually just the folder for the current type of document. i.e. - if you select a pages document - and select iCloud from the Path Bar - it will show you ~/Library/Mobile\ Documents/com~apple~Pages/Documents

So if you want to see all your iWork documents you can make a smart folder. Go to ~/Library/Mobile\ Documents -> Then in the search bar type in tef
Seems that all the iWork documents use tef in the name. Then you can use the save from the search bar - to put that search in your sidebar. For other Apps - it seems they have a different identifier that varies app to app.

If anyone else has better ideas on how to get to the iCloud documents I'd love to hear it.