My first server was a Windows Server 2003 running ActiveDirectory and Network Home Directories.
My first Linux server was Ubuntu 6.06LTS. I ran Linux before, but never as a server. My 6.06 server ran a web server, MySQL databases, and a MySQL-based media server. It also ran VMware Server 1.0. Everything was done via GUI but I learned a lot of Bash Scripting and doing things over SSH.
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Finally, everything has evolved into my production level servers.
My Dual Xeon E5520 box runs on RHEL running CrashPlan Pro server (enterprise backup), VMware Server (running Windows Server 2008 and 2008 R2 virtualized for ActiveDirectory and Printer Sharing, along with RHEL, CentOS and Ubuntu 10.04 LTS virtual machines.) running Matlab, Apache, Ruby-on-Rails w/ nginx/passenger, NFS sharing, and a Media Streaming server. It has a GUI installed but I don't use it. I just SSH in to do anything. Or locally I just use X to have multiple terminals on the same window.
My Mac Mini runs Mac OSX Server 10.6 running OpenDirectory/LDAP, Network Home Sharing, Printer Sharing, Wikis, and Remote Desktop Task Server.
My E3200 runs a gateway server based on CentOS handling NAT, firewall, and a few other basic services. Has a Web Interface but every advanced requires manual configuration.
My Atom runs NexentaStor for ZFS file server/backup server. No GUI.
I even rent out from RackSpace Cloud for CentOS, RHEL, and Ubuntu servers running webservers, proxy servers, and mail servers. No GUI on any of these suckers.
GUIs are great for learning. You have a web browser for testing your services, even space for multiple terminals and text editors to multitask, rather than one terminal session per session. But overall, I find it more efficient to use my workstation to SSH into all of the servers to do anything. You learn a lot by fiddling with config files, and BASH scripting.