iirc, OSX behaves in the exact same way as Ubuntu. Alt-Tab, to switch between applications, and Alt-something to switch between windows of an application. I could be wrong though, it's been over a year since I used OSX now...
Every time I have to put my hands on a friend's Mac (to show/help/diagnose something) the single most frustrating issue is trying to alt-tab between multiple windows within an application (mostly browsers). I do it, and instead it goes to another application.
I have asked every single one of them for such a hotkey get blank stares, and reluctantly use mouse instead. All of my Google-Fu never helped much either.
While we're on the topic, is there a hotkey to toggle maximize/restore of a window in OS X? I was impressed with the way Windows 7 handled it, so much so that I've emulated it in all of my various Linux configurations.