Is there a keyboard shortcut to jump directly to a particular full screen app in Lion?
If you want this for a specific app, you could use an application like Keyboard Maestro to set up a shortcut to switch to that application.

If you want this for every app, I don't think it is possible at the moment. It may come with an update (as the ability to manually re-arrange spaces in Mission Control).

Waiting for a better solution, you can still use ⌃→ and ⌃← to navigate between spaces (including fullscreen applications).