I can see this working with 'trusted' areas.. of course it's a bad idea in a coffee shop or office with lots of people you don't trust.. but at home or your own office this can be really time saver.
In which case, your machine may also be hibernating, which is slow to being with. So something like automatically unlocking while your phone is around isn't really all that useful.
Not to mention, how long does it take to type in a password?
On a tangent, I'm really excited about this and hope there's a Windows+Android version on the way (or clone)...