The big plus to the software is the amount of different file formats it can import. RVT are one of the very few file formats that can not go directly into JetStream (there is currently a plug-in for Revit if you have a copy of JetStream). I would be very surprised by the time Revit 2010 comes out, that there won’t be a direct export from Revit, and or JetStream being able to import rvt files.
The other big plus is JetStream being able to link in a Microsoft project file and assign different component to the construction program. This allow you to do clash detection of the construction process itself.
JetStream is currently being used to coordinate Oil Rig so our building are easy in comparison.
Have a look at the workflow demo on the NavisWorks website. I’m not sure if Architects will use JetStream itself, but it is an ideal tool for the contractors.