We do municipal water/wastewater treatment and distribution consulting. AutoCAD's really our only choice for interaction with our clients. (It's also the only CAD package I've used since '94, so about the only one I know now.)

As far as Civil3D goes, it's ok, but not ideal. At a company where I used to work, we'd used AutoCAD LandDesktop. When AutoCAD first released Civil3D, it still included the LandDesktop companion so we continued with it for a couple years. Around 2004 the company I was with made the Civil3D switch. Some features were better (primarily roads), but most were a little more clumsy.

LandDesktop kept most of the data in external files, so the actual drawing file was still pretty lean with just the resulting points, contours, profiles, etc. With Civil3D keeping everything in the drawing, it bogs down quicker on large files. The idea of keeping everything as dynamic entities is nice, but can ruin a lot of work previously done when one item new item fails to resolve properly and corrupts a surface.

I got used to Civil3D over a couple years, but then went to work privately with a few other engineers who were still using LandDesktop. It was odd to go back to an older program and realize how much quicker/more productive work was with LandDesktop.

Since LandDesktop companion was discontinued a couple years ago, we did make the Civil3D switch. It's better than it used to be, but I'm still not sure the pros outweigh the cons versus LD (or other similar packages) .