If the issues with having to look at dark areas are common and persistent in the consumer release, it'll kill mainstream adoption. A geek might dislike having to do it, but they'll do it, but explaining to most people "oh sure, you just look at a shadow and hey presto" isn't going to convince them.

I'm cautiously optimistic about the product, I just hope that Google can nail these issues before they release it, otherwise wearable tech might get a bit of a bump back in terms of adoption.