Thanks for the feedback. We do have this feature, but its somewhat hidden. We will make sure to make it more prominent in future.
When you list a bucket - the default view shows virtual folders and files. Click on "Show Full Path" button and that will show "raw" listing like JetS3t. Then you will also see a "Filter" option. You can type the first few characters and hit "enter" key to see the filtered list.
Do like a search so i can see which ones aren't set and then set them individually. Instead of having to select all and then set the ACL and wait for the whole list to be sorted through - whole list = 50,000+ files