In what cases is unified inbox relevant ? I don't like to mix my personal emails with my work emails. Did sparrow make a clear distinction between which accounts the email was from ?
So the reason I use a unified inbox is that I only have to login to one place. I can then choose (using the filters) what work I'm going to concentrate on - eg I might look at the support@ addresses, or my personal ones, or all the addresses of one company/project. It can take a while to learn the use the filters well so you're not presented with an overwhelming list of everything but I'd hate to go back to individual inboxes now :)
I know Gmail lets me pull all those into one inbox with account importing, but there's a limit on those too. Maybe it's just time for me to simplify all my accounts :/