This is how I wish app switching worked on an iPad with a Bluetooth keyboard, as I wrote here: prolost.com/ipadkeyboard
Command + Tab, with optional arrow keys. Just like Mac OS X.
Tap this combo rapidly enough and you don't even see the app switcher, you just jump to the next app.
If you'd like to see this implemented, please go here and request it: apple.com/feedback/ipad.html