Documentation, documentation and more documentation.. The life blood of IT. The only problem being that it is very difficult for a technically minded individual such as myself to write documentation with NO technical content what so ever! These documents are what the business really want; They do not care that the workflow capabilities of SharePoint bring easer workflow to the masses, they only care that it is there; They do not care that we will be deploying on 2 front end servers with 1 application server and a database server for the first initial farm, they only care that it will work.
With this in mind how do you impress upon them the potential of the system? Well... you don't, you can only build a system with the capabilities that you think they will need and once you get down to the details of migrating their applications will you actually get any meaningfully feedback..
That is the advantage of using SharePoint. It can do pretty much anything: If not out of the box, then you can build on it, or get contractors to work on it...
Its all about standards...