From my perspective and that of my friends, the traffic is very poor quality. We have burnt huge sums with MIVA UK and USA over several years and, despite utilising their targeting features, the traffic converts abysmally compared to the Tier 1 PPC search engines.
With MIVA USA, for instance, we selected to receive no traffic from Europe for some of our websites, but were still paying for lots of visitors from low grade sites in Romania and Russia.
Worse thing is things are deteriorating...