I've been getting over 31 consistantly.
Go to
www.************** select Fuel Econ. from the menu and login as guest, choose the nissan sentra from the list. It brings up a list, mine is the first '08 with all the mnts entries. That's what I've gotten in the first 3k.
And no, break in will make no noticable difference. The only difference people "see" is their getting accustomed to the way their new vehicle drives. It's natural to get easier on a car as you drive it. Unless it's a Spec-V of course
BTW NO econo class vehicles need breakins, heck most non performance vehicles don't for that matter. Hemi's do though