I noticed that duplicate entry titles currently throw a slim application error, which I never want a client to see. I can tell them to never post an entry with a duplicate title, but inevitably that will happen, and the slim application error screen is not something they should ever see. It is not helpful at all, and does not explain the error in a clear way.
Ideally, entries that are sorted by date can have duplicate posts if they are on different dates. For example, I have a client that wants to do TBT posts with just the title "TBT". She can't do that.
If that isn't possible, the system should, at the very least, throw a simple error message clearly on screen explaining that there is already a post with that title and that they should choose a different title.