Finally did my first gig with my F-50 this weekend. I didn't want to bring my main Mark IV along as a "backup", so I brought my POD-XT along and figured I could go direct if I had to. I also brought a spare set of 2 used power & 2 preamp tubes.
Luckily nothing happened, but I was still sweating bullets. I've had a critical piece of gear fail on me only once before onstage, and it was enough (I very stupidly brought only one guitar to an out-of-town gig, and the low string broke, throwing all the other strings out of tune... you try playing "Under a Glass Moon" on a single string!).
In any case, I'm going to be picking up a 2nd Mark IV for at-home use, and make my other Mark IV my primary gigging amp (with the F-50 as a backup). I'd just rather have something I can switch to quickly on stage. Having a head, combo, and 2x12/4x12 cab is a pretty redundant combination. The only thing I wouldn't have a backup of is my G-Major (if it failed the only real victim would be those weird pitch-shifted RATM solos).