My Garmin counts every small rise along with the "real" hills. That's the same method most mapping sites like ridewithgps.com use. Most of my riding is in SW Ohio and nearby Kentucky and Indiana. We have lots of 300 foot high hills here, and the rest tends to be rolling instead of flat.

So far this year, I have 3,020 miles and 150,400 feet of climbing. That's 49.8 feet per mile. In 2011 I did 55 feet per mile. The rule of thumb is that 100 feet per mile is a "hilly" ride.