Maybe there are 2 faces to this: current users and acquiring new users. First one has been discussed in other comments: current users do not want to relearn th

Maybe there are 2 faces to this: current users and acquiring new users. First one has been discussed in other comments: current users do not want to relearn the UI of the software. And I second that. Second one: new users may turn away quick when seeing an old UI when trying an app or web site for a first time. So moving the UI from old to new, from time to time, may be a way for an app / website to just survive, otherwise the user base may be eroding. Thoughts?