Best way to inform users after file upload I'm searching for a good solution to inform users after a file was uploaded (with standard upload URL: ...file/add).

I would solve this with rules, but I can't find the right events for this.
Has anybody a good idea.
Have you checked out the Entity Rules module? I believe this is exactly what that module is for. 

I did a brief check and you can create a reaction rule on a Create Entity action and then check the type of that entity.