My opinion on flourocarbon: Not saying I am know I'm right, just my thoughts through experience and what I've learned from fishermen much better than I...
For fly fishing (mainly in still waters) for picky trout esp in clear water with small flies, I use flourocarbon leader/tippet. I'm not 100% if I catch more fish with it that with mono, but the last couple years I've had great success on lakes with my leeches, chronomids, etc and I was always using flourocarbon. So, for this application I have confidence in it and use it.
For river fishing, I think it's mainly a waste of money. Last year I fished mainly flourocarbon leaders for coho and not once did I outfish the other guys with their mono leaaders. I think it comes down 99% to what/how your using (esp the size of the hook/lure), and if it's being fished effective/in the stike zone. I fished beside my buddy all day several times and he always outfished my flouro with his mono. Why? He is just more experienced at fishing his set up just right, quicker on the hook set, etc. If all variables were the same would flouro possibly come out on top? Possibly, but given its cost and the amount you go through in a day, 9/10 days on the river I'm sticking with mono leaders. If nothing seems to be working and fish are there I would switch to flouro as a last effort.
I also noticed with flourocarbon the knot strength sucks compared to mono. I had several improved clinch knots bust at the knot with a fish on. I did some research (knot wars on You-Tube) and found that the improved clinch is not a very good knot with flouro. Switched to the palomar and noticed a big difference. However I find the palomar a pain to tie. Overall my take on flourocarbon is there are certain applications where it may give you an edge, however most of the time it's poor knot strength and high cost make it a less than practical choice.
One last thought on using flouro with spoons, jigs, etc. IMO if a fish sees a big spoon or similar lure in front of its face the last thing it's going to notice is your mono leader (assuming you're fishing a reasonable lb test). If fishing a tiny hook with, say, a jensen egg in clear water? Perhaps it may give your an advantage, I just haven't noticed or seen from other guys any difference. However if you watch any fishing show it's flourocarbon or nothing! The exepnsive Seaguar type too, of course...