Eh, I think the seat actually helps keep things organized. I put heavy, boxy things on the seat, lighter, bulky things in front of the seat, and bags and whatnot behind the seat. Mine looks something like this, and has the coverings and everything so things stay dry.

But I don't use it for carrying cargo every day, it's more of an occasional thing. If we go together, we take the car, otherwise I'll try to take the bike so I get some exercise at the same time. If I did it more regularly, I'd probably get a proper trailer with a higher weight limit. But my city isn't really designed for cargo bikes (bike paths/lanes aren't near shopping areas, few proper bike racks, etc), so even if I had one, I probably wouldn't use it enough to justify it. But the kid's bike trailer is perfect because I live right next to a nice bike path that goes to a small fishing pond, so I'll take the kids with quite often. But even when the youngest outgrows it, I'll probably keep the trailer for hauling stuff.