He has 70 assorted models for termigaunts and hormagaunts, but mostly it is his hatred of vehicles. The absurd price of carnifex doesn't help either!
Vehicles are relatively easy to deal with, provided you don't mind spending money. Hive guard are quite points efficient at inflicting bunches of glances on most things, even heavy venom cannons have a new lease of life now ap - isn't totally lame. What you cant do is shake/stun things into submission any longer. I like Zonethropes too, but they have short ranges.
Carnifexes are still quite good, but you need to keep points down to less than a Trygon. Why do I get the feeling that you know all this already though Philly?
What kind of build you going with on the dark eldar front? I have never played as Dark eldar, but I have played against them quite a bit.