The hot/active/week/month tabs were only removed for anonymous users. If you're logged in at all, you will still see them. I think my meta-post covers the reasons behind this (mostly simplification for drive-by users).
Also, we have put a lot of effort into simplifying our accounts management over the last year. We're about halfway there, but at the moment we aggregate site accounts under a global account. You'll have to take an affirmative action to "join" another site, but it's not the whole registration process - no separate username/email/password.
Bottom line is registration requires an email and password, and that gets you the key to all of our sites. You just have to "use" the key on the site when you interact the first time.
Also, I'll add that you could just go here: http://stackexchange.com/questions?tab=hot