For those fans of the steep and deep there's a pretty interesting thread covering this subject on Epicski.com right now. One guy is even posting slope steepness stats down to the tenth of a degree for many famous Eastern expert runs. But as we know, snow conditions, trail width, bumps, trees and other factors all come into play besides just sheer steepness.
Here's a photo taken at the entrance to Rumble, a tough, narrow run in the steep Castlerock trail pod at Sugarbush, VT. Fresh, young legs come in handy here: http://image58.webshots.com/158/8/20/85/394482085rAcIQd_fs.jpg
The line between "natural/ungroomed" trails and true backcountry terrain gets blurred at places like Mad River Glen ski area in Vermont. I guess if you can get there from a lift without a lot of hiking it qualifies as a "trail"?? This shot of Paradise at MRG depicts a fairly conventional looking expert trail, but unseen hazards such as cliff bands bisect the area: http://community.webshots.com/photo/260653519/260653519UNKlsX#
More in-bounds, but all-natural Eastern terrain; Face Chutes near the top of Jay Peak, VT: http://community.webshots.com/photo/299232570/299278150OyvLhv
In recent years Cannon Mountain, NH has officially (albeit rarely) opened some tough terrain under and near their Aerial Tramline. Here's a shot of some guys roaming around this stuff with a serious vertical drop to Interstate 93 below: http://community.webshots.com/photo/300503683/300503683KbLvcs
Another shot of certifiably sick glades visited by this group: http://community.webshots.com/photo/300542278/300542278OaMCrx
I'm impressed with any snowboarder that can maneuver through this sort of long, steep, tight, bumpy glades.
Their semi-inbounds excursion occurred in the vicinity of the lift line shown in this shot from Cannon tram base: http://community.webshots.com/photo/296383748/296387198QTaaGz