The common wisdom was always not to rely on it for any of your users (for far too long) and build something separate as soon as possible. But i must admit that lately it got much much better. I only recently discovered that you can have multiple admins with it's own admin models.
So way less hacks.
I actually want to try build an app just to see how far I can push it with Django admin and see how hacks it will end up.
I haven't seen it used by users, but it's amazing for non-technical staff (PMs, support to some extent, etc). They can inspect and modify the database while making sure everything still validates, run batch jobs, actions, etc and it's all very low effort to implement. No need to fetch a dev to debug an issue with data or understand whether the cron job run or why it may have failed. It helps with understanding a platform's internals, which improves understanding and communication all around.
I actually want to try build an app just to see how far I can push it with Django admin and see how hacks it will end up.