Hi Bruce. As Micheal suggested, many people like to use MoI in conjunction with Rhino because of easy data swapping. Another thing to consider is that Rhino is developing many tools which are well-suited for architecture :

Explicit History (graphical node-based scripting, can drive parametric models)
Paneling (parametric paneling of surfaces and polysurfaces)
Archcut (parametric Floorplate and Building Sectioning)
VisualArq (parametric floorplan and 3D architectural modeler)
Flattening aka "Squish" (flattens double-curved surfaces into 2D patterns for manufacturing)

More info can be found on the Rhino Labs page:
http://en.wiki.mcneel.com/default.aspx/McNeel/RhinoHomeLabs.html

This is all in very early development, so it will not be a replacement for something like Revit. But it is something to watch in the future. And you can use all of those tools now (in open beta). Also there is the huge price difference between these packages which make it very easy to outfit many users with MoI and Rhino:

MoI = $195
Rhino = $800
Revit Architecture = $5,500

jonah