In preparation for Lion, I ran the ‘Find Orphans” option in AppDelete.

As expected, about 30 orphans were discovered. As AppDelete allows the orphan list to be sorted by date, a few of the really old orphans (going back to 2002) were easily deleted.

All remaining orphans are plists. But I do not know which ones are safe to delete. Is there a rule of thumb or some such that provides a bit of insight? I am not looking for a guarantee, just general counsel, advice, and gotchas to avoid.

I'm not familiar with AppDelete but I assume it uses a mechanism similar to CleanApp or TinkerTool System to identify related applications and is reasonably accurate. Normally if a necessary property list (.plist) file is deleted the application will simply generate a new one the next time it is launched and the only damage is the necessity of resetting your preferences for that app.

If you are feeling super-cautious you can move the suspect orphans to another folder and/or compress them. If they reappear after a period of time then some app is using them and you can either continue to use the new plist file or replace it with the one you moved. If they don't regenerate after a reasonable length of time then they probably truly are orphans and you can delete them.

If your files are other than property lists you might zip the file in place and see if anything quits working. It it does then unzip the file and you are back in operation, If nothing breaks after a while you can simply delete the zipped file.

By-the-way CleanApp does have a feature that some people find reassuring. It maintains an online database of files that users have deleted along with a given application and when it reports potential files for deletion, it tells you which files others have deleted along with that particular app. Personally I am not sure how much reliance I place in the other users, but there it is.

Many thanks, JM. I had forgotten about archiving stuff prior to deleting, so indeed I am pleased I asked, and even more pleaseder that you responded.

Another feature of CleanApp is the ability to archive, archive and delete, or just delete applications/files at your discretion.