mine has a few key differentiating factors, which I think will make it a great service.
1. built on top of a solid SOA. this is still in progress, but with a proper SOA, keeping up with all the different carriers' online functionality should not be a problem, and developers can be assigned to certain carriers, and to implement the carriers' functionality into the larger shipping management product that we are building. In addition, SOA based on WS-* standards will allow our offering to be incorporated into BPEL processes, which many larger companies will undoubtedly be using in the future.
2. low cost. we use open-source technologies, which makes our software costs approx. 0. I'm almost positive, should demand go as high as I'd like it to, to deploy on Zend Platform, or ActiveGrid, and to use commercial licenses of MySQL, Linux, etc. besides just the software licensing, the popularity of the OS technologies means there will be a huge number of developers as potential employees.
3. relating to a project Matt has going, I will also work on a RAD framework with him that will, hopefully, be built with consideration of allowing developers to quickly and easily set up communications with services such as the one we'll be offering. if that really is the case, then popularity of that framework will only help to accellerate the demand for our service.
4. federated identity. I don't know a LOT about this (yet), but the concept sounds great, and it's one of the differentiating factor that the Rearden group uses. hopefully Rearden will eventually be one of our customers. =)