Can you explain to me how one would risk never being able to root again by going back to the stock rom? I'm not trying to be a smartass, but I've seen several people say it and I was wondering the reason behind it.
To best explain this, we start from the beginning. No one has root to the Evo. Hackers start analyzing the software on the phone poking around for weaknesses. In an ideal world, all software is perfectly secure, and there's no way to gain root access. But in reality, nothing is ever 100% secure. Eventually someone will find a way to obtain root access.
From there, that person will develop a separate program/process designed to exploit that weakness so that other people can easily obtain root access. Utilities like unrevoked, simpleroot, etc were created so that we can all break into our phones and make the changes so that we keep root access. Without these pioneering hackers to discover the exploit, no one would ever be able to root their phone.
Once an exploit is discovered, it can be fixed. So typically when you update your phone with a new release, a fix is part of that release. Once you're updated, and the fix is in place, you won't be able to use that old exploit anymore. You now have to wait for a hacker to figure out a NEW exploit on your current version of the software. There's no guarantee that a new vulnerability will be found, or how long it will take to find it. That is why there's a chance you might never be able to root your phone again.
If you are currently rooted, you don't want to accept a stock update for 2 main reasons:
1) the stock update expects an old stock build. A rooted phone is not a known state for the phone, so the update may get confused by something and crash. That creates the possibility of a bricked phone.
2) assuming the update works, it will overwrite the system files that give you root access. To get it back, you have to hope that a hacker can break into the updated version.
If you are currently rooted, and you really want the features of the upcoming stock update, the best thing to do is SIT TIGHT. You don't even need to wait that long. The difference between a stock rom and a rooted stock rom is very minor. The developers and/or hackers can package the "root" with a stock rom very easily. This process DOES NOT REQUIRE a hacker to break into the new 2.2 system. Doing things AS ROOT is much easier than trying to OBTAIN ROOT.
In most situations, you don't want to give up your root powers. The only time to do it is if you are in a situation where you need to take advantage of your warranty.