Home Shopping and Energy Consumption

[viscousmemories]

Ever since I read this great post by lisarea, I've thought a lot about this line:

Are you contributing to the depletion of the atmosphere and limited fuel supplies by ordering things over the internet and having them delivered discretely, rather than using the more efficient methods of transport afforded by the distribution methods employed by big box store chains like WalMart?

At first I thought, "Wow, that's a really good point. I've bought a bunch of stuff online that I could've gone to Walmart for! What was I thinking?" But the more I think about it, it seems like it might even be more energy efficient to order things online. After all, I'm sure UPS is as efficient as Walmart at getting stuff from the manufacturer to the local distribution points, but then one UPS truck delivers goods to 100 places instead of 100 people driving separately to one place for the final delivery.

What am I missing here?