We have the old Peapod LT, the black one
, and it definitely gets in the way of cargo. Our plan was to have the four year old sitting stoker in front of the seat, and the two year old sitting in the seat. But we also want to tow a kid's bike, so the Peapod can't be all the way to the rear. It makes for a challenging fit, and we ended up getting a different seat, a custom-made Roundabout
so that we have a seat without legs. Now we have three rack solutions -- the Peapod on a flightdeck, the Roundabout, and the original Snapdeck. The Peapod is the best for sleeping in. The Roundabout is great for cargo; it doesn't cover up the freeloaders and you can fill the seats with stuff if you don't have kids along. The snapdeck is best for carrying an adult passenger or really big cargo.
We chose to have our Roundabout built with Superhooks, and the Peapod Flightdeck has them as well. So these racks take a few minutes to remove (you have to unscrew four bolts with an allen). The snapdeck is faster to remove. We had extra holes drilled in our Peapod by the bike shop that set it up for us so that we could un-bolt the flightdeck while leaving the Peapod attached. So really we swap decks rather than seats. I think the Peapod was a PITA to remove from the flightdeck, but I don't remember. Still, presumably you'd be looking at the newer Peapod, not the one I have.
At this point, the Roundabout is our default seat, with the best match of cargo space and kid space. I have not tried the new Peapod III. They say it has a higher position that helps free up cargo space. I'm not sure about that; it still looks like the feet extend pretty far into the cargo space.
If you contact Rob Hanson through his flickr account, you can get a quote on a custom roundabout seat. In addition to doing two kid seats, he said he's also done a rack that combined a single seat and a trail-a-bike mount. A roundabout seat probably costs more than one Peapod, but less than two.