Today there was a seminar on IBM Workplace solutions at Hilton Singapore. It was a half day seminar and it pretty much talked about Lotus Notes/Domino, WebSphere Portal, and IBM Workplace.
In brief, what i understood is that IBM Workplace is not a replacement for Lotus Domino. Infact, when you already have Domino up and running, you just don't have to do anything except to be in the upgrade path 6.5. Eventually you will get to IBM Workplace when both the product line merges.
In other words, Notes/Domino is evolving and soon will become a J2EE compliant under IBM Workplace technology. Domino server will soon become a provisioning server and can manage its own client components based on the role a user has got.
It also means that some of the offerings under IBM WP like IBM Workplace Service Express is for the new customers who don't already have Notes/Domino or a Portal Infrastructure.