I've tried the app with mixed results. Here's what it recognizes and what it doesn't:
0-40%: It recognizes my face but it also unlocks the iPhone to (pictures of) Charlie Sheen, Jessica Alba, Richard Dean Anderson, Laura Vandervoort, Barack Obama, George Bush, Fredrik Reinfeldt and Amanda Tapping (conclusion: unlocks for everyone).
40-65%: Only unlocks for me, pictures of me, Jessica Alba and George Bush.
65-75%: Unlocks for pictures of me and for me.
80%: SOMETIMES unlocks for me, unlocks for pictures of me.
100%: Doesn't even unlock for the picture of me for which I did a training set. Conclusion: doesn't unlock for anyone.
While the practical uses are very limited, I have to admit that it is a cool tweak. Hopefully future updates will make it better.
Edit: I tried it with my face, one picture of my face and 8 random celebrities.