Several people asked about Dutch-style long cargo bikes at Interbike. An American derivative of this is the Zigo Leader shown here. The child sits in front of the adult in a detachable carrier that doubles as a jogging stroller.
This is a pre-production model you’re looking at, and Zigo is still working on getting dealers for their bike. I’ll get more details later, but I suspect it will be sold mostly through sporting goods stores and online.
The Zigo Leader is actually a decently designed bike — surprisingly lightweight, 8 speed hub gearing, and disc brakes. It handles nicely — much better than pulling a child trailer. I don’t know what the weight limit is, but it looks like this can be easily converted to also carry cargo.
You can see more information about the Zigo Leader, including a video and photo, at MyZigo.com.