Any hill steep with traffic, or where I hit over 45 mph, or with sharp turns at the bottom make me nervous. Sometimes it is just exciting, though.
There are lots of hills around here I don't like to go down around this time of year. Too many wet and slippery leaves on the road for me. I'll go down those hills after the leaves clear off the road after the first good snow. I also don't like it going down steep hills when there are icy patches on the road.