One of GRUB's greatest strengths is its robust design -- don't forget this as you continue to use it. It's not necessary to reinstall GRUB if you update your kernel or change its location on disk. Instead, just update your menu.lst file if needed, and all will be well.
There are only a couple of situations where you'll need to reinstall the GRUB boot loader to your boot record. First, if you change the partition type of your GRUB root partition (for example, from ext2 to ReiserFS), a reinstall will be needed. Or, if you update the stage1 and stage2 files in /boot/grub so that they're from a newer version of GRUB, you'll most likely need to reinstall the boot loader. Other than that, you're all set!
There's a lot more to GRUB than what we covered here. For example, you can use GRUB to do network boots, boot BSD filesystems, and more. In addition, GRUB has many configuration and security commands that you may find useful. For a complete description of all GRUB functionality, be sure to check out GRUB's excellent GNU info documentation. Just type "info grub" at your bash prompt and read away.