How to downgrade an iOS app for iPod touch?
If you have Time machine enabled or you don't empty your trash very often you're in luck. You can go into Time machine and simply roll back to an older version of the app in Finder. Then if you uninstall and reinstall the app from iTunes you'll get the older version. Apps are stored by default in /Users/YOURUSERNAME/Music/iTunes/iTunes Media/Mobile Applications if I'm not mistaken. Just find the older version in your trash or hit Time machine once you get to that directory and roll right on back.