This Lotus Connections Technote was pointed out by Handly Cameron on Twitter:
Question
What procedure should be followed when an employee leaves an organization where IBM Lotus Connections is implemented? Should those users be deleted from the Profiles, Dogear, Activities, Blogs applications?
Answer
Once a person is entered into the Connections system they should never be removed. Doing so may invalidate the data’s consistency. For example, In Activities, the log for who did what and when that action was performed relies on the member information always being present. If users are deleted from the database, the log entries will not be unresolvable.
This is true for Connections 1.0.x and 2.0. It does go on to say that this has been reported as an SPR and is under investigation, but even so, seeing it written in such black and white terms is a little worrying. I can see this being a showstopper for many organisations. Not good.