Having been in the Information Technology field for over 15 years, I can completely understand long, long days.... and all nighters. They are no fun for anyone. I can also appreciate improving systems by placing them on a better platform, implementing a more robust security mechanism, and making them more appealing.
It is a simple fact that typically we, humans, do not like change. We are creatures of habit and find comfort in what we know and find familiar. There are, however, many measures that we (as IT professionals) can take to ensure our users will not experience such a shock to a new way of doing things. By not preparing the users..... you will, inevitably, receive much negative feedback. Who can blame them?