See this is what I don't get about Google.
There are thousands of problems that Google Glasses could solve. But life recording and answering how long a bridge is are terrible use cases. For me it makes far more sense to position it in firmly in the business and education sectors. And then provide the necessary back end services to support developers.
It ties in so much better with other Google services and works to their strength which is in solving big data problems. Leave the gimmicks to the others.