I already use GMail's Priority Inbox to separate "Important" from "Not Important" messages. It works pretty well and with the split screen view it's not that big a deal if it miscategorizes something.
It's the same with the Updates tab. I get that Facebook and Twitter are really noisy. But I want the updates I'm currently getting to go in my inbox. That's why I haven't unsubscribed from them.
It could be that Gmail is optimizing for the lazy of us. That's my view on the Updates tab as well: I have unsubscribed from a bunch of this stuff, but I keep getting more of it, sometimes from new sources, sometimes from existing sources but new accounts, and other times from existing sources who have added new kinds of notifications my previous opt-out doesn't respect. At some point I gave up fiddling with it and just got used to the x# sequence (default Gmail keybindings for select-and-delete). Gmail putting it into its own tab is a net improvement in user experience for me, because now I can xjxjxjxjx# all at once. I might even give a brief glance at the subject lines, so they aren't necessarily useless. But I don't need to read them as emails, and I don't need them interspersed with my real email. Conceptually they aren't really emails, but an email serialization of a status update, like what you find under the little red number icon in Facebook. So I like them being shown as such, in a separate space.
It's all filters I could have set up myself, but the default filtering pretty closely aligns with my preferences, so for me at least it's working. And so far, Google has actually never moved out of my Inbox any email where I've opted in to receive the email. The only things getting filtered are things I never asked for.
Perhaps, but having filtered tabs for Promotions, Updates, Social and Forums is fantastic.
Most of the time when checking email, I only want to know if something urgent and personal has come up. I can read the mailing lists and newsletters once a week when bored.
It's the same with the Updates tab. I get that Facebook and Twitter are really noisy. But I want the updates I'm currently getting to go in my inbox. That's why I haven't unsubscribed from them.