Is there a way to apply a biometric lock (as in, a look screen) to an Android device? e.g. the unlocker has to pass a fingerprint / retina / voice scan. I've read about startup companies and general ideas, but haven't seen any actual product.
Some phones have hardware built in for such things. For example, my Motorola Atrix has a fingerprint scanner to unlock it, http://www.authentec.com/a/ATRIXFAQs.aspx. Also, like you pointed out, Ice Cream Sandwich is going to have facial recognition for locking/unlocking.
It's possible to develop one, but we don't have pixel-per-pixel touch screens(like the one that the second generation Microsoft Surface uses) on our Android phones, so it will not be accurate, nor even trustable. What may be out on the Market are lock screens that imitate those systems, but they are just for visual effects.
The only example that is valid is the face-recognition, the iris-recognition I don't know, but I think this needs a lot more improved technology. You can check out BioLock To Bring Biometric Security (Iris Scanner, Facial Recognition) To Android for more information.
I am currently using an app in beta called Zwypelock. This app learns your unique behavior — the way you hold you phone, the pressure you apply to your touch screen, etc. It lets you unlock the phone with just a swipe.
Here is the link