I live in Campbell and ride mostly on private land but recently became a member of trailpass, they have several riding areas in our area and several organized rides throughout the year. check it out at www.trailpass.com
When I think of Western NY, I think of the Buffalo area.
That being said, your area is pretty nice. I like the Bath/Hammondsport area, myself. Haven't hit the trails there, though.
ETA: I just realized that I responded to a thread that's 3 years old.
I guess there AREN'T any good riding areas in WNY.
I've been riding the gas line and in private woods on existing ATV trails. With deer season coming up in less than a week I'll leave those woods alone until after Christmas. I'm looking at joining a local club near here, plus my Dad owns 40 or 50 acres of woods to the south.