I use mono exclusively....why? Because I think its sounds tigher. In a band context with another guitarist, its difficult enough to find sonic "space". Stereo yes sounds wider but that depth can work against you.
Persoanlly ( and this is a real sweeping statement) I'd only use stereo live if I was a single guitarist and the focus was on effects ( more ethereal/indie music). For straight ahead rock, mono...
Agreed on you V8guitar, I use an "in between" solution. I am a single guitarist in my band. I have a stereo setup but my mostly used sounds are without any modulation effects. The stereo delay in leads is really just for fun stereo. So you can say i play mono most of the time. But those specificly rare modulation sounds do much better in a stereo setup.