Today i changed my Entry Listing Default from "7 days" to "Entries" , and as a result MT deleted ALL entries for the past 7 days from the database!!!

MT 4.01 has some serious bugs relating to publishing - especially dynamic publishing - from my personal experience of the last 3 weeks I strongly advise against updating to MT 4.01 for high-traffic/ commercial blogs until Six Apart have identified and fix these bugs.