I'm definitely biased more in favor of convenience and shipping speed. But to take a recent example, I just bought something last week on eBay, and regular shipping was free, or I could upgrade to USPS Priority Mail for $9.99. For a $32 boxed set of DVDs, this triggers my rip-off sensor, even if it's not enough to really matter. And it wouldn't be two-day shipping, just priority mail. Good but not the same.

I like eBay well enough and I have my quibbles with Amazon (especially the marketplace) but they definitely have the one-click-and-you-have-it-tomorrow game nailed.