Wondering if most people have GNOME or KDE installed on their server, and how much memory do these guys consumed.

I have been running a VPS website with only 256MB of RAM fine, though memory does appear to be a bottleneck at times. So got a new server with 1GB RAM but I'm surprised to see after installing CentOS 64-bit with GNOME the memory consumption varies between 600MB-1GB.

The only difference is I've never had used any GUI desktop on the VPS (don't think the hosting company offers one). Wondering if the memory consumption came entirely from the GNOME desktop I installed.

Would most people install with GNOME, configure all the stuff required, and then remove it? What's the best practice?

most professional sysadmins would not use X windows at all on a server. You might install the client libraries, but actually running GNOME or KDE on a server should be a big no no ever. You should certainly never ever leave the system logged in and running anything like this, as that's clearly just a waste of resources.

Is there anyway to say, shut it down, after using it and leave it there available to be turned on again if required?

On a personal home server running Slackware I have fluxbox and xfce installed, simply because it was more trouble than it was worth to remove them from the installation. On occasion I find it useful/easier to do some things via a GUI so I start up an XDMCP session (the server is headless with no keyboard or mouse of it's own) and do what I need to do, and then drop the box back to a non-graphical runlevel. If the GUI isn't running it's not using any resources, although it might still have some cache. 99.99% of the time though it is running sans X.

To be more specific to the question, yes especially if you set the server to boot into the console so that you have to explicitly "startx" to get a GUI going. I don't know exactly how you would do it in CentOS. It's the default in Slackware.

Generally speaking I'm alright to use pure Putty to do everything. However, I'd like to have the option to use GUI if required. Can you tell me how I can set it to not boot up with GNOME by default? And if it's already up, how can I turn it off without having to reboot?

just edit /etc/inittab to boot to runlevel 3 not 5 by default. I can't remember the exact line, it's like "id:5:initdefault" or something. Then "startx" will load the desktop all shiny style.