stampmagnet
SME is a fully preconfigured version of CentOS with all services installed & enabled (or ready to be enabled via GUI), and after a fairly quick CD install it is ready to go out of the box in it's designated full server role (refer write ups for functional feature list "out of the box").
It also has a purpose specific server GUI manager panel, but also has a text based server manager.
It can be controlled by novice admins using the GUI panel, or via command line for more competent users, or where additional functionality or tweaking of settings is required (ie beyond those offered in server manager).
The other neat feature(s) is the templating & db system which allows easy change of settings, and quick restoration to default values.
SME could be called "an easy to use CentOS" for the equivalent roles.
Did you also read
http://wiki.contribs.org/SME_Server:Aboutand
http://www.theregister.co.uk/2010/11/17/review_sme_server/