I first came across this when I tried to redeem some of my 100k miles I accumulated on British Airways from business travel (at the time AA/BA didn't give AAdvantage miles for transatlantic flights on BA).

Almost any time I try to book an award ticket, I'm hit with, for example, an $800 ticket that "costs" $250 with $550 in fuel surcharges. This results in award tickets that cost 50,000 miles + $550. Definitely not worth it and not what I was expecting when I signed up.