If you had to explain to someone what being a Christian meant to you, would you include the concept of Hell? Clearly for some people, this is an important reason for being a Christian - perhaps even the most important reason? However, I think that there are two key difficulties that become quickly apparent when talking about Hell today.
The first is that most people simply don't believe in Hell. I suspect that this includes most Christians if you really push them on the subject. Certainly they don't believe in Hell as the literal place of eternal fire that is pictured in classical literature and art. There's all sorts of reasons for this - a better scientific understanding of the world we live in and the historical context of the Bible among them - but this isn't even the main problem as I see it.
Believing in Hell says something very important about what you believe about God. What kind of God creates Hell and condemns people to eternal suffering in it?
For me, the central components of Christianity are the Cross and Resurrection of Jesus. The Cross says something equally important about the nature of God to me: it says that God is non-violent. When the non-violent Incarnation of God comes into conflict with humanity bent on power and control, the Cross is the inevitable result. The Resurrection is a proclamation that ultimately violence cannot win.
Hell, however you conceive of it, is a violent concept. Therefore, to threaten people with Hell is to inflict spiritual violence upon them. Such wrongly conceived evangelism is, as I understand it, a deeply unChristian act. Can we really expect to have it both ways? Either God is wholly violent and condemns His own creation to damnation or God is holy, unviolent, the source of love, mercy and compassion.