I have a standard configuration Yuba, and I love it. I want to address some things raised by other folks:
1. It is one-size-fits-all, but I'm 6'5" and it's totally fine with the 500mm seat post and adjustable stem.
2. While it's true that the Yuba isn't compatible w/ Xtracycle stuff, I have found it very easy to customize with clamps, ratchet straps, and other regular hardware and bags and things.
3. The stability under load is pretty spectacular - I've hauled a 170-lb person easily, and I routinely schlep my two children and $250 of groceries at once.
4. The ride is pretty agile. When not under load, it moves just like any hybrid.
5. It's cheaper.