the only people i've seen use a passcode are teenage girls, and users with a corporate email policy that require it.
That's not what I'm seeing. I only know one other person who doesn't use a passcode, and I know a LOT of iOS users.
I still don't use one because I don't want to look like a d***** and because if someone steals it, not having the passcode will increase the chance that he will use it without wiping it or anything and let me track it down with Find My iPhone. Let's face it, your friends would do more damage with an iPhone with a passcode that they somehow get into than an iPhone that is trustingly left unlocked. Plus, if I lock it, I have to disable Siri at the lock screen to be secure, and then it's just inconvenient. To put this into context, I don't have any sensitive data on my iPhone.