I've never used one...but went to a show recently and saw a friend using one. Let me tell you....this thing sounded amazing! I'm sure that it helps that the guy was a great guitarist. But still....I was amazed at the sounds coming from the V-Amp. The optional midi floorboard is really cool for live performance. I'm gonna pick one up!
I used it on a mic'd tube and as well as solid state. Sounded 'full' on both. I used it also for gritty/screamy vox and it turned out pretty good. I would send you to links to some songs, but honestly my mixes probably wouldnt' do it justice. If you want you can pm me and I'll link you anyway.