I play a lot of live shows and have used Elixir Nanoweb strings for around 2 and a half years. These strings are marginally more expensive than the Martin ones I used previously but they last about 3 times as long.
The only negative I can give really is that the brightness you usually get with a brand new set of strings isn't quite the same with these, almost like the Nanoweb coating is deadening that tone slightly. Don't get me wrong, these strings sound GREAT! Obviously the brightness I'm referring to only lasts a day at the most on a non-coated set of strings before they start to deteriorate. I can get 4 or 5 gigs out of a set of these if I need to whereas I used to change after 2 gigs.
Totally recommended by me!