Thanks for this great info. I totally agree with you about there being so many threads out there on how to root the EVO. Even if some threads are ultimately referring to same method of rooting, if you don't read them carefully, you might get lost and think it's just another different method. Because everyone has their own way of describing the process.
The EVO is my first Android phone, and my previous phone is the PRE as well. I also rooted the PRE (via command-line Linux method, ughhh) and used the WebOSQuickInstall tool to add customization, so coming to the Android world of ROMs, Unrevoked, etc was all new and different for me. I never understood the idea that rooting an Android actually means replacing the whole image of the OS (ie. installing a custom ROM). Your post above made it all clear to me, and I now understand why there are so many ROMs being passed back and forth and updated, etc.
I guess this is analogous to how I used to create image backups of my entire Windows OS back in the day using DriveImage or something similar. With Windows 95/98/ME/2000/XP, installation never works right the first time, and especially after installing drivers and apps, and I kept on having to uninstall the OS, reinstall the OS, then reinstall drivers, then apps, etc. I got sick of this so I decided to create an image of the entire OS right after I installed the OS and drivers. So later if I had to re-do the installation process, all I had to do was install the backed-up image file and this gave me a clean and readiliy available OS + drivers to start with.
But anyway, I have not installed any custom ROMs on my EVO yet. All I did was root the EVO using UnRevoked3 (and it put whatever ROM it came with on my EVO). Now, I'm just deciding whether I want to replace it with another custom ROM. This one works fine for me currently, dont see anything wrong with it.