Where Google has succeeded is to offer a free service (search, maps, email, android/mobile os) that was either initially or after feedback best in class. And they successfully monetised those products (not so easy vis Twitter).

However, Glass is different. It requires users to pay up front for the service. This is inherently a different model for Google. Adoption is not free, nor just a click away. It will be interesting to see if/how Google succeeds in getting this right (as it will likely precede other forays into hardware).

Fortunately for Google, they have huge cash flows and plenty of cash and talent lying around, so Glass does not look like it is at risk. Having said that, it may take years before adoption (in whatever form that is) will be accepted.