I used to love using big marshall stacks, valve heads, now I have the FM3, I've yet to take it out on a show, but I know Metallica, Def Leppard, Maiden, Aerosmith, etc.. all have ditched their valve heads..
interesting story, the day I got my FM3, I was so overwhelmed, I couldn't find a sound that I liked... after I was blaming the gear saying, "It's too complicated, I'll never get my head around this..." my wife turned to me and said, "well, it's good enough for Metallica..." and with a wry smile she turned around and walked out the room.
since then, I have taken my FM3 out once or twice on a gig, and every time it's just been amazing, even the stock presets are just insanely good.
for sheer ease of use, personally, I'm going to hold onto my valve gear, but I know where I'm headed, FAS all the way.