In case you hadn't heard about it, Amazon recently introduced an all-you-can-eat expedited shipping plan called "Amazon Prime."

At first I held back signing up for it, figuring that I often qualify for free shipping anyway. And people that buy a lot from Amazon knew the secret -- that standard shipping often arrives in two days, even without paying extra.
But then I thought it through -- if you order more than $300 or $400 dollars a year on Amazon, the $79 pays for itself on shipping costs, not even counting the usual additional cost of 2-day shipping. Plus, if you really need it overnighted, that's just $3.99 per order (normally a lot more). Now you no longer will need to wait until you have $25 in one order before qualifying for free standard shipping. And as a bonus, you are allowed to invite your family members to share in your Amazon Prime plan, giving them free expedited shipping as well. Insane.
So for $79/yr you can enable 1-click shopping with free 2-day shipping (it works for normal, non 1-click, shopping-cart orders as well). This potentially changes the way you shop. Figuring that most things can be bought a day or two in advance, why not just find them online and hit "1-Click"? The total cost will be as low, if not lower, to finding it in a store, and you don't even have to deal with the hassle of going out. Plus, if you're smart you would have comparison shopped the item on Amazon already anyway (for the reviews and recommendations, as well as for the prices). So once you're there, this makes completing the order there almost automatic.
For example, I just bought my father a copy of Gödel, Escher, Bach. I found it, added it to my cart, hit "1-Click", selected his address, and I was done. Total cost? $9.80. (Well, it was $15 but I happened to have a $5 rebate for something that I didn't even remember buying. That and the secret bonus discount.) He'll get the book Monday. I spent 60 seconds and less money than I would have in a physical store. Nevermind the fact that they're in Maine and I'm in California, so I'd have to ship it no matter what.
I'm not sure anyone else can match this offer. Amazon can only do it because of the absurdly optimized logistics operation it runs. While I can't say anything that isn't already public, Amazon is simply a lot more cost-effective and efficient than anyone else, online or otherwise, at getting products out the door.
The downside, and this applies to free standard shipping as well, is that third-party sellers don't qualify. So you need to double check to see who is offering the item. It's understandable -- Amazon can't control the costs of third-party logistics -- but it is still something to keep in mind.
Since Amazon launched years ago, I've been using them for books and cds and other small gadgets. They basically defined e-commerce, but it was still distinct from the space of all commerce. With Amazon Prime, I'm pretty sure I'll use them (and not a brick-and-mortar, nor an Amazon competitor) for just about anything they carry.
For what it's worth, I'm not just saying this because I work for A9/Amazon. I tend to be fair and critical, and will certainly shop around for the best deal. But I'm honestly impressed with Amazon Prime. And not just as a customer -- I'm also impressed as someone who sees how projects like this get done. This company is constantly pushing itself to do things better than the competition. The culture is one of innovation and of success. People actually care about what they are doing and about the people around them -- it's night and day from other places I've been. Amazon Prime was a no-bullshit product from start to finish, and I believe that fact is reflected in the value it offers to the customer.
And, lest you forget it, we're hiring (just had to throw that in).