The oddest thing I've noticed about it is that if you double click to go into the app switcher, the app you were currently in isn't the one with the main focus in the app switcher.
No, the previous app is. It's a sensible default, the one you're most likely to want to switch to (means you can quickly switch between the two, alt-tab works the same way in Windows (don't know about on OS X as I use Expose or whatever it's called these days)).
Another feature that helps with that is the "Back to ..." you get in the top left now when you've followed a link from one app to another. Eg, open a link in Mail and you go to Safari, and now there's a "Back to Mail" button on the top left.
I like the new switcher. Feels right.