I figure after you update the kernel you want to reboot immediately, but are there other things that you can update safely without having to reboot?

Is there a way to tell which ones should have the server rebooted after you install and which don't need it? looking at an up2date on one of my rhel servers, i see things like firefox that need an update which i'm sure i can do without rebooting, but the other 100 updates i'm missing, who knows.

I never reboot anything except for a kernel update. Every other service on my Debian box (except Xorg) stops the service, updates, and then restarts. I do manually restart Xorg (CTRL+ALT+Backspace) if it gets updated.

OK, thanks. I was kinda wondering if it was only the kernel that would need a restart after updating.

Strictly speaking, it's just the kernel. The rest of the things can be stopped and restarted when there's a need to reload them (so the updated version is used instead). However, sometimes, 3rd party drivers will force you to reboot. For example, unloading the fglrx graphics driver and then loading the updated version can sometimes hang X when restarting, so you need to do a full reboot. But those are -by all means- boggus drivers, something that theoretically shouldn't happen. Most kernel modules can be unloaded and reloaded without any problem, as long as there's nothing using them at the moment of course.

Great, thanks.