Nobody likes to find a good deal that ends up being a bad one because of exorbitant shipping costs. In the jungle of online retailers indexed in Google's Product Search (formerly Froogle), nothing is more common. To solve that problem, Google has begun a voluntary program for retailers to include their shipping and tax information so that potential buyers can see what the total cost will be before clicking.
The new system runs through Google's Base product, letting retailers note whether they charge tax. It's also set up to let them set tax and shipping amounts by location so that the price will change based on where the searcher is from.
On most deal sites like Slickdeals or Fatwallet you'll see people work this out on their own--Google is just taking that extra step out of the equation, which could make it even easier to find a good deal without surprises. As an addendum to this feature, I would love Google to cross-reference its product index with a rebate index to let you save that much more on bargain goods.