> we're going to be using a Windows Service to host our WCF services and message bus (I think Gary already wrote it ... I haven't looked at it yet though).
>

Permissions is usually the biggest issue I've run into. I was testing a WCF hosted in a command line app (which made it easy to see what was happening during development) that worked great until I moved it into a service. At that point things started failing, mostly related permissions (and a few related to the default directory). So permissions is now the first place I start looking when I develop a service.