here is a link to a thread with multiple topics that you might find interesting regarding root.
http://www.droidforums.net/forum/droid-hacks/11102-all-one-popular-threads-read-before-posting.html
You don't HAVE to use any ROM. The device can be rooted w/ superuser and you can leave it at that.
If you choose to, you can load ROMs, Kernels, themes, etc.
some good links...
http://www.droidforums.net/forum/droid-hacks/632-what-root-means-stop-asking.html
http://www.droidforums.net/forum/rescue-squad-guides/39254-sbf-root-unroot.html
and each ROM will have install instructions.
http://www.droidforums.net/forum/custom-roms/
fyi, rom manager can be found for FREE on the dev's webpage.