Cpanel is part of a two headed monster - WHM - Web Hosting Manager is the part used by the admin. Now of course, for real
sysadmins it is a bit of a joke! But for those, like me, who are not sysadmins but are thrown into the job, it is a godsend. It manages many aspects of Apache, Bind, module provisioning, system security and account management for hosting
Cpanel IS the user level interface and gives control over the users creation and management of MySQL databases, email, webmail and includes rudimentary file management. It reduces support costs by allowing users to do a lot without having to call tech support and have them do it!
For general hosting machines I use WHM/Cpanel, it is reasonable cost and certainly does speed up the management of a hosting operation.
For other machines I use Sugarbox ( http://www.inter7.com ) with vpopmail and vwebmail. This allows me to use my preffered Qmail mail server, but only on machines where there are no other users.