Damage to the contact surface on the flywheel isn't normally the issue unless you've let it really go one it's started to slip, Neil is right with the dual mass bit, with these the flywheel is effectively mounted on rubber connectors which give a little when you engage the clutch, it gives you a softer engagement, but on most cars these rubber mounts wear, I've had a flywheel go on a focus st (at 47k miles!) where the mounts just gave up end result was the remainder of the flywheel went bang, replace the fly at the same time for piece of mind