I burned images of ClarkConnect 5.0 and SME Server 7.4 and have been evaluating them. For some reason I cannot get comfortable with the ClarkConnect 5 web interface. I guess it really does not matter because the 10 free user account cap is a deal killer. Per the Clark Connect website:
"By default, the Community and Enterprise Editions include 10 accounts that have groupware/mailbox functionality. The Enterprise Edition is upgradeable to 250 users (in units of 5) by purchasing additional mailbox licenses from Point Clark Networks."
I have SME Server 7.4 loaded on an old Dell OptiPlex GX110 and it is running fine. The interface has a dated feel to it. It seems to have all the feature that my brother-in-law is immediately looking for and has additional features he can grow into.
e-box looks like it has been under heavy development since the last time I looked at it. I plan on downloading it soon. The interface looks great and it may give SME Server a run for its money.