Here's an interesting link from a person who has used both the BoB and the Extrawheel. I was heading toward the Burley Nomad, but am now planning on buying the Extrawheel. There were three compelling arguments:
1) It is much lighter than the Burley and, therefore, easier to cart through airports and hotels.
2) The Extrawheel is a single-width, as opposed to a double wheel that is a constant concern for roadside obstacles.
3) It uses regular panniers, which are more water resistant than the Nomad according to some users.