Filter / Select Edited Photos in Lightroom

Your photography workflow probably looks something like this:

Take way more shots than you could possibly edit; lament the required hard drive space for the 15-20 shots ultimately worth editing
Flag the best photos for actual editing (just press P when viewing the photo in your Lightroom library)
Filter to select only flagged photos, and then actually edit; skip over some flagged photos which don’t look as good as you remember them

Back to the Library: Filtering for Edited Photos

Now you want to filter the folder to just the photos you actually edited. Here’s how:

Start out in Library mode and select the folder you want to filter
Open the Metadata filter
Set one of the column headers to "Develop Preset"
Select all of the values except for All and Default Settings (use control/command + click to select multiple options)

Done! You’re now viewing just the files with edits. You can select multiple, export all at once, move to a different folder, etc.

You can also use Smart Collections to select all photos with edits, although this solution is slightly less elegant

Back in Library, select your new Smart Collection and you’ll see all photos (ever) that you edited
Select all of the photos (control/command + A)
Click on the folder you want to filter
All photos from the folder will be visible, but the edited ones will be selected

You could now add these photos to the Quick Collection for further editing or exporting.