I've heard that they are quite easy to administer though they have a somewhat limited range of utilities and applications. It seems like a odd question to ask since you say that you already have Lotus Notes installed on an existing UNIX system. If you have needs for customized procedures or specialized hardware then UNIX is probably the easiest to adapt. Unfortunately I see far too many cases where selections are made before requirements are understood, and where the selection process is constrained by organizational politics more than by requirements analysis. The real job of a consultant is to assess and analyze your requirements and provide recommendations to match them.
Consultants provide consultation.
Thanks for your input. We are on Sun Solaris now and the application is quite stable. At least from my point of view. Requirements for 3rd party software are an issue with UNIX and the Lotus Notes application. Your input has helped.