If you're Canadian, you may simply be remembering incorrectly as Amazon.ca used to be $39, but also changed to $25 a few year ago.
http://www.amazon.com/gp/help/customer/display.html?nodeId=5...
I apologize for the error.
But since getting Prime I've had things show up the next day. It's sort of freaky. I trialed Prime for the VOD aspect and I bought some product or another, forgetting about the delivery thing. And BAM it was at my house. I got that "I could get used to this" feeling.
In most cases I appreciate having whatever it was I ordered ready for use sooner, but I'd have to give some thought to whether it really makes all that much difference to me, especially since I'm not using the VOD thing as I expected.