I'm curious who here actually uses Zbrush for hard surfaces. Some of the new features recently added in 3.5 make it much easier to create hard surfaces from scratch, but I don't see too many people using this work flow.
I find Zbrush (and now mudbox does it rather well too!) is great for making bio-mechanical stuff. Hard edges on nicely curved surfaces. But when it comes to things like engines or cars or guns and etc, modelling is definitely the way to go. That's my personal opinion though!