While building new apps I keep thinking of the quote attributed to the CEO of Black & Decker: “People don’t buy our tools because they want one-inch drills. They buy them because they want one-inch holes.”
As technologists we think about the guts of things, but customers often favor the simpler thing (Twitter, Mac OS Spotlight) over the more conceptually powerful one (Google Wave, WinFS). My career’s full of this: advocating general, interesting stuff (e.g. HTML layers for Photoshop) only to get pantsed by simpler approaches (just tweaks to the existing PS vector tools).
I’ve heard that Amazon starts projects by writing a press release of what features the user will see, then working backwards to check that they’re building something valuable. We’d do well to do the same. As Einstein said, “If you can’t explain it to a six year old, you don’t understand it yourself.”