I can tell you with mine that I have shut it off in just over 2 years. At night time I just flip that litte mute switch on teh side to make it go silent, but I never turn the iphone off or power it down. There is no need to do that.
Surprisingly the battery doesnt drain at all like some thing either, when it goes dormant like that, in the morning the battery power is basically the same as when I went to bed. The only time its actually been turned off is when I upgrade iOS, because then it powers down and turns itself off automatically to reboot, but thast the only time I remember having my iphone off.