It happens to us all: an application update for the iPhone or iPad goes awry, and the new app doesn't do things the way we want (or, unfortunately, work at all on one of our devices). We ourselves are in that boat at the moment, since the new version 2.0 of the TUAW iPhone app is not working as expected on the iPad -- our development team is digging into the problem right now and we hope to be fast-tracking a fixed version right away. Our apologies for the issues.
This sort of thing is particularly sticky because there's no Apple-supported way to roll back to a previous version of an iOS application once you've updated. There is a workaround, however, if you haven't yet emptied your Trash in the Finder (or if you can restore your Mobile Applications folder using Time Machine). Read on for the steps.
The first step is to check if you've emptied your Trash or not. Open the Trash in the Finder and look for piles and piles of .ipa files -- those are all the recently-updated iOS apps, and the older versions have been placed here for deletion. Grab the TUAW app .ipa (184.108.40.206) and drag it to the Desktop. If you have emptied your trash, check your backups for older versions of the TUAW .ipa file.
Next, open up iTunes and look in your Applications list in the library. Click on the current TUAW app version and hit Delete. You'll be prompted to either keep or delete the app file -- you can choose Delete, then go back into the Trash and rescue your 2.0 version .ipa in case you want it later.
At this point, sync your iPad so the newer app gets removed from the device. Then, just drag your 1.0 .ipa file into the Library section in iTunes. Voila! You can now sync back the older version to your iPad.
The catch, of course, is that you can't have both versions syncing independently to your two devices -- so, as mentioned, our app mavens at Aol will have a fix for the iPad crashing as soon as we possibly can and they'll ask the App Store gatekeepers for expedited review to get it cleared up.