We've been gradually turning on the Web Mail 6.0 interface for a few thousand users at at time and soliciting feedback so that we can fix any problems before rolling it out 100%. We'll be doing one or two more test batches and then hopefully turn it on for everyone with in the next 3-4 weeks. I previously posted more information about the new interface changes here.
Here's a live screenshot:
If you want to be in the next batch of users who get to try it first, let me know here and I'll put you on the list. During this period we have a link that allows you to opt back out if you have trouble.