Mono fishing line definitely shines in some situations. For heavily pressured fish like in the lakes around my home near Milwaukee I use 4lb mono sometimes with a 6lb fluorocarbon leader. I really dislike fluoro but use it when I think it's necessary. Also use mono exclusively when crappie fishing. The extra stretch is a little more forgiving on their "paper mouths".
Light superlines (6-10lb test/1-4lb dia.) like Fireline have three characteristics that I find extremely attractive. First they are very forgiving to line twist, something that is the scourge of mono. Second, It has incredible sensitivity and as ST says require a simple wrist flick to set a hook. In fact in the early days when I used it I was setting the hook far too vigorously and losing fish. I had to train myself to take it easy. When trolling with Fireline there is no hooksetting, it's completely unnecessary. And third, the stuff seems to last forever and does not seem to deteriorate in UV light like mono does. Attention must be paid to the last 3-6 feet just as with any other type of line because it will get nicked,cut or frayed with hard use.
In short, I find the characteristics of Fireline Crystal so desireable that I will use it when ever I can. Many times I like the fact that it is more visible than mono. My eyes are not what they used to be and when line watching during low light cloudy days it's been a real asset. Also makes knot tying easier but have a good pair of clippers handy, it can be tough to cut.