The idea of a smart watch to mean always seemed like one of those things that made a great concept but would never really be a practical thing to have in everyday life. Products like the Lunatik looked cool but had major drawbacks like no wireless communication, not waterproof, poor battery life (compared to a traditional watch), and you had to press a button actually see the time.
Newer projects like the Pebble are interesting for nerds, but are still more like a proof-of-concept than an actual product. It is a cool idea that no one will actually want to integrate into their everyday lives.
This piece Bruce Tognazzini marks the first time I have ever really been excited about the idea of a smart watch. He outlines lots of things that will be useful for individual uses (my favorite being eliminating passwords), be he also presents some ideas on crowd sourcing data provided by millions of people wearing these watches could benefit the general population. Examples include improving mapping and providing data for numerical weather prediction.
It is a long article, but it is very interesting. I recommend checking it out.