So, the problem with your exclusion of "non-simple CRUD apps" is that simple CRUD apps have a nasty habit of ceasing to be simple. But yeah, case in point: I

So, the problem with your exclusion of "non-simple CRUD apps" is that simple CRUD apps have a nasty habit of ceasing to be simple. But yeah, case in point: I ran a small BB-style web forum a number of years ago. As it grew larger (on the order of 10k posts - hardly earth shattering for a web forum), the load on the server got unsustainable, and the page loads were really slow. It turned out that the algorithm to decide if a user had seen a post was to maintain a list of seen post IDs for each user, and compare them at each page view. For active users, the number of seen posts obviously approaches the number of posts: n^2.