I think ideas like this are fantastic.  As Marketing Pilgrim noted, the idea is pretty simple:

"If you have a cell phone that is compatible, you could point it at the bar code and go to a web site printed at the bottom of an ad"

This is interesting from a high level for a couple of reasons:

1. It marks a continued shift to make information easily accessible, any time any where, and as a result is continuing to lower the transaction costs of shopping.  I for one know that if they added these bar codes to the bottom of Us Weekly photos, and my fiancee ad the right phone, our credit card bill would be about $100 more each month
2. It also shows another example of how mobile technologies are going to change all of our lives.  I often think of the current state of the mobile as analogous to the internet in the mid 90s.  In the 90s the first companies to go online basically took their old business model (catalogs) and pasted them statically online and it wasn't for 3 to 5 years until the more innovative models were developed.  Similarly now most companies are simply trying to see how they can make their current service available on a mobile device, instead of being innovative in the space.  This product by Google is a good example of a company thinking outside the box to come up with something unique.

That said, I'm not convinced this is ever going to be hugely popular.  It would require lots of people to adopt a hardware that is barely available today, which takes time.  I admire their approach though and look forward to more things like this as Google rolls out its Android product.