There is no reason to change the interface. Ever.

I use Yahoo mail everyday for business. I have an established work flow that I've been using for years. Changing the interface, just for the sake of change, is like leaving your house for work, and when you come back, someone has replace your house with a completely different one. It still performs the exact same functions, except nothing is where you expect it to be. Please leave it alone, or make it VERY apparent where the old interface is. I don't want to have to go on a treasure hunt to find it.