I rooted and stayed Stock for a while because it let me uninstall apps that I normally could not uninstall (Amazon MP3 and Google Goggles).
However, now that I rooted, I just decided to install Enomther's ROM and am SOOOOOOO glad I did. I have a black status bar (hate the white and there is also issues with it burning into your screen), easy Spare Parts app that allows me to uninstall unwanted stock apps, download the HTC camera app that allows for 720p video recording and other stuff that I like to mess with.
All in all, root and try out custom ROM's.
Just remember, unless there is a major update that you fixes issues you have, you don't have to re-flash every version that is released...
[How-To] ROOT Your Nexus One without Unlocking the Bootloader. ALL ROM'S!! - Google Nexus One Owners | Google Groups