There's something to be said for mechanical simplicity and one gear may be enough if it's all flat. It is a bit crazy to have 18+ gears on a regular road bike. I mostly only use a few different ones on mine.
You need some hills to get your heart working!
!BEER
good point about the hills, we just don't have them here though! I think the 18+ gears was maybe spawned out of competition because 3 speeds were fine but then someone said oh yeah, we have 10! Normally on these many geared bikes you have 3 on the front and 6 or 7 gears on the back tire but when you change the gears on the front the difficulty in pedaling or is that torque? I dunno, but it changes dramatically I would say too dramatically. Especially if you are downshifting on a hill this can be something that is actually dangerous. But then again, maybe I just suck at it :)