That's an excellent question, so much so that I was going to start a thread on it myself.
The local bike club grades rides on terrain rather than speed, with a few exceptions. The ratings are something like this:
1 - 0-25'/mile. Flat.
2 - 25-50'/mile. Rolling.
3 - 50-75'/mile. Hilly.
4 - 75-100'/mile. Nasty.
4+ - >100'/mile. Might as well be mountain biking.
Most of my rides are in the 40-60'/mile range. Riding on the flats is a treat and doesn't insult me in the slightest. Unfortunately the only place that is flat locally is downtown and I don't care much for urban riding.
My most severe road bike rides are around 90'/mile, and I'm pretty beat after them.
There are no sustained climbs to help the numbers here. The highest is about 375' at around 15% grade.
One of our OCD hammerheads actually tabulated every single worthy hill within 50 miles of here. I reckon I've climbed about ten of them. Here is the site if anyone is interested:
http://www.louisvillebicycleclub.org/climbs2.htm