Seth Godin explains on his new book blog, The Dip, that the web has changed the face of purchasing by providing more choices and competition than we've had in the past:

The Dip by Seth Godin: The Best in the World imperative

ACCESS: Because of the web, we don't have to limit our choices to the Yellow Pages or who's nearby or who was recommended by a friend. As a result, with far more choices, we can pick the very best choice, not the most convenient one.

However, one area where the web is still behind the curve is local convenience. When you're making a significant purchase, choosing between competing products or professionals can make a huge difference in price and quality. But what about times when convenience and speed are the top priorities?

What if I'm looking for a more commodified service, like a towing or locksmith? While there still may be differences in price and quality, the key factor isn't price but speed in situations like this. Can the web help me quickly figure out who will arrive quickly to solve my problem?

Or, local product searches. More than once, I've forgotten something important while traveling such as a phone charger. Again, price isn't the key factor, and the product is comparable from any store, so I just need to know where I can find an emergency replacement as fast as possible.

Things are getting closer faster for retail than professional services. For example, Google can plot cell phone retailers based on distance from a zip code:

Eventually, I'd like to be able to search by product rather than retail category and see results of stores with the charger I need in inventory. We're not there yet.

Put another way, the best choice isn't always the best quality or cheapest, but simply the most convenient. Web enabling this type of choice is still far from done.