I've owned one for three years. I agree with most all that has been said about it by other owners. I will add a couple of things. though.
I have never been a fan of EL34 power tubes for bass. They break up to early and seem to lack low end oomph. In the VB-3 there are eight of them. Ruby EL34 BHT's I believe are stock with this amp. These tubes are definitely a cut above your average EL34 when it comes to clean headroom and freq. response. I proved it to myself when I tried 4 of them in a Peavey Windsor amp head I had at the time.
But after corresponding with Bbbybld, the amps designer, about trying 6550's (no can do), at his suggestion I tried a set of EHX large bottle 6CA7's. This brought the amp into a whole new and wonderful (to my ears, anyway) world of tone, clean tone. Closer to 6550's, but with their own, unique voice. I highly recommend this upgrade. Honestly, I don't know why these EHX big bottle 6CA7's aren't the stock tube.
I also tried a set of TAD 6L6GC's, while it wasn't my "cup of tea" tone wise, it could be for some people. By the way the bias scheme is set up for that swap.
Also the resonance and presence controls allow a wide range of tonal palette, although it might be too much twiddling for some people.
I agree with what was said about the knobs being on the cheap side. I will say, though, after opening the amp to swap the tubes and have a look around its vitals, I saw that the chassis and pcb's are typical armor plated, bullet proof Peavey. If I was gigging this amp regularly I would probably change the knobs to something more deluxe, just because...