So far I'm enjoying it...a lot of people have said that the interface is like Yahoo's, just slighty better. They took it that one extra step.
The biggest difference though is the "conversation" thread. I'm still sorta figuring out how it works exactly, but it groups e-mails that are part of the same thread of communication all together and you can open and collapse messages as you go. And everything's searchable.
Problem is, I don't know what to use my account for just yet! I've got two spam accounts, a mailing list account, my personal account, my professional account, etc...