In addition to directly signing off to ZZZ's post above, I would like to state an additional key concern with the combining of Business and Personal notebooks: There are no more owner contexts.
Let me explain that (not that the Evernote Team needs this explained): When I'm looking at my own personal notebooks, the tags list on the left pane shows only tags from my personal notebooks. When I'm looking at notebooks shared to me by another Personal user, I see only their tags. When I'm in a Business notebook, sure enough, just Business tags.
Now they're all mixed. I'm drowning in tags
Also, a note to the rock stars at the Evernote Windows team: We complain because we love Evernote. Thanks again for everything.