Zope + Plone vs. Lotus Notes for groupware and workflow

We are currently in touch with a very large corporation that faces
a an internal discussion about which platform to choose for crisis
management groupware and workflow. Fear, uncertainty and doubt make Lotus
Notes the default choice pushed by the IT department. But the department
that represents the actual users have had experience with Zope + Plone and
they love it. The problem is that they don't really know how to translate
that into a convincing case that will win the decision makers to their
cause against an IT department that is widely perceived as a jurassic era
relic.

Openness toward heavy customization, ease of integration and connectivity
with other tools, timely bug fixes, availability of talent for hire are
all known points, but we need to develop them further to make them easily
understandable. In addition, we need to support our case with well
respected references that will impress conservative decision makers.

The target application is quite sensitive. Crisis management means complex
workflows that have to operate under extremely strong pressure and allow
the organization to operate coherently in a chaotic environment. The
customer has deep knowledge of his needs, so we need only worry about the
implementation : how may Zope + Plone be a superior platform ?

I guess that the the best way to find out is to turn toward the people who
have the actual experience. We have implemented our Intranet (a small
hundred users) with Zope + Plone but we would like to hear from people
with more serious stories. So if you wish to help push your favorite
platform toward a new large user base, please share what you know that
could help in building the conviction of our prospective customer.