Unite and Widgets are being removed. These are 2 awesome ideas, sadly underutilised. I hope some of the Unite applications will show up as extensions (I think the extensions API can be improved to offer similar functionality). Not really sure if/how Widgets can be accommodated in the extensions API.
I'm waiting for the release too. I've been using Opera as my primary browser for years, and now I'm using it as my mail client as well.
I love it, but hate that it doesn't support some CSS3 elements, and doesn't have hardware acceleration.
But that's set to change with Opera 12.