Rather than go into a massive web page about it, I'd rather spend time on the actual script. I'll just include some basic information here.
Please note that the script is not fully tested. Please make a backup of your system before you use this. There is a chance that this script could delete files that you wanted to keep.
Current version: 0.83
Here's how to install it:
Here are the files from the package if you want to see them online. In all honesty, you could just download the actual buildkernel script. It'll make much more sense and be more useful to you if you at least skim some of the documentation.
If you have suggestions or questions, please email me at wstearns@pobox.com. I will be putting together a mailing list for buildkernel announcements as well. Let me know if you'd like to be on that list.