I've been riding for a little over 2000 miles. Stock bike, I'm about 150-160 lbs. I'm in NYC, and about 2/3rds of my riding is commuting in the city itself or riding around in Brooklyn, with about 1/3rd being weekend rides to Bear Mountain and such. According to my GasTracker app (which I highly recommend):
City: 66%
Highway: 34%
Average Lifetime MPG: 33.7 MPG
Best MPG: 62.8 MPG
With so much city driving, and with me being more aggressive than many, I'd say this is pretty well within normal for a 750 CC bike. That best number was clocked on a long NY highway during the Gypsy Run, we were pulling 80-100 for most of the way.
When I baby the bike for a tankful in the city, I can maybe get 30 MPG, but NYC is just all stop and go all the time, and it's mostly short trips. When I don't baby it, and I'm out with friends ripping around Williamsburg, I probably get 26-28 MPG.
YMMV, heh.
Addendum: At the end of January, I'm moving from NYC to Denver, CO. I've also installed a VH Slip-on. I'll update in about 1000 miles, but I expect that my mileage will go up, with less congestion and more highway riding.