I would like the ability to change the names of Contacts, Companies, Opportunities or any other major entity. There are some organizations that would like to call Companies Accounts. There are some that would like to call Opportunities Deals. I'm sure you can think of others.
Right now in ACT you can change the field names and labels, but it doesn't really propagate throughout the application. The ability to change entity names would give ACT more flexibility and adaptability to work in a variety of environments and match what the customer refers to them as.