I must say that is news to me...
Yep, I am running leaked version of ICS on my Bionic and have done several reverts to stock GB followed by manual applying ICS again and have had no problems. My Xoom was running a custom ICS ROM for months but I reverted back to stock to try the OTA build. All have easily been rooted thanks to amazing developer support in the community. It is sometimes possible to cause problems if you do something wrong but most of these root methods have gotten extremely easy these days.
If a person can read and follow instructions rooting a Android phone can be as easy as 024.... . :-) I've rooted my N1, Atrix, Inspire, Skyrocket, and GSII. By doing so I've been able to get the latest and pure Android OS update well before ATT released its bloated versions. I've been running ICS for a few months before the "official" ATT release.
Glad to hear you guys had successes with rooting...however...
As a senior Moderator on an large Android site...I can tell you that I have seen literally thousands of crashed, significantly messed up, and bricked units from rooting. Even several other Moderators who know how to successfully root caution against the practice, except for those willing to see problem results.
The biggest challenges include multiple ways to root, multiple "tools" to root (there are over 15 rooting toolkits out there right now for ICS alone), and incompatibilities with installed apps that cause rooting to go haywire. In plenty of cases, it took weeks and weeks to recover for people. In other cases, there was no recovery until a full original install was done (painstakingly). Note: these were not all rookie users either.
That prompted my comments that rooting was risky, and I stand by that...even if some other folks do it blindfolded ( a minority of users).
I've successfully upgraded through 7 newer versions of Android on my tablet, and 3 on one of my phones, using the prescribed process. Never a problem with that technique.
ICS had less user rooting than previous versions, mostly because it included capabilities that prompted rooting in earlier versions. I suspect Jelly Bean will continue that pattern. There seems to be less and less reasons to root as Android versions advance. Still...some will do so anyway, despite a shorter list of motivations to do it. That's all OK, as long as folks know the risks.