There must be a way to log in as root at boot, but how? How awesome would it be to be able to set it up with multiple users!
iOS is unix-based... You do not want your iPhone always running with root permisions. This would be a HUGE security risk.
As far as I know, you can't login as root except through SSH. If all you're wanting is multiple profiles, I think that's what Mobile Profiles from the Cydia store does, but it's not free. It's a $4.99 app with a free demo.