from the screencasts, it looks as if it takes a number of taps from the launch of the application until you finally reach your inbox. - the latest screencast shows the user first select an account, then a folder and then finally the first list of messages shows up.
We will see in the final version, of course... But, with the new idea of Application Windows, Menu Views, and Sub Views, this may be what we're "stuck" with (it's just something new to get used to, I guess). But, I do know that a lot of care is being taken to reduce the number of clicks that it takes to get to a final destination, so there is some hope. Still, eradicating submenus and adding Sub Views inherently increases the number of "pages" that users will have to view in order to do something. A positive aspect of this is that everything will occur very fast.
Tim
http://samoff.com