The hills in Pittsburgh are extreme, but not hugely long. There is a local race called the "dirty dozen" where you race up each of the biggest hills. I ride up an 8% everyday to work not so bad compared to these. On some of the hills your front wheel wants to pop up and do a hill induced wheelie.
http://www.dannychew.com/dd.html#anchor003

Here is the list of the big hills and some other tidbits from the local press.

1. Center Ave./Guyasuta Rd. in Aspinwall
2. Ravine St./Sharps Hill in Sharpsburg
3. Berryhill Rd. between Saxonburg Blvd. and Middle Rd.
4. High St./Seavy Rd. in Etna 5. Logan St. in Millvale
6. Pigg Hill/Rialto St. across from the 31st St. Bridge
7. Suffolk/Hazelton/Burgess Streets on Northside
8. Sycamore St. on Mt Washington 9. Canton Ave in Beechview
10. Boustead St. in Beechview 11. Welsh Way on the Southside 12. Barry/Holt/Eleanor Streets on the Southside 13. Flowers Ave./Tesla St. in Hazelwood

According to the local newspaper
"Canton Street in Beechview is the steepest street in this hilly town and, probably, the region, with a grade of 37 percent -- that is, rising 37 feet per 100 feet of run. So confirm records from the city Department of Engineering and Construction. "


Also from the article:

Figures can be fuzzy, but the best San Francisco can do are grades of 31.5 percent. The world's steepest claim is made by Baldwin Street in Dunedin, New Zealand, but its steepest part, according to the town's own Web site, is only 35 percent. Could Pittsburgh have a world record hidden in the trees high above Banksville Road?

http://www.post-gazette.com/pg/05030/448976.stm


Some of the most extreme hills that I have biked are--
Shenandoah national park range from 1150' around 4050'
The road up to the Grand Tetons from Jackson Hole. Something like a 10 mile hill.
The road up to Hogs back (Amatole Mts) in South Africa from Alice Something like 10 miles an 5000 feet. (Alice is where Mandella got his law degree at the U of Fort Hare.)

Cheers!