Remember when I rooted my Vibrant? Just recently CyanogenMod 9 (based on ICS) nightlies started being built for the Vibrant, so there's no better time to go ahead and jump up to bleeding edge CM9, right?
My only concern was jumping from the Bionix-v ROM to CM9. I have heard some horror stories when switching between custom ROM series. So just to be safer, I went through the CM7.2-rc1 release candidate as an intermediate step.
It was fairly painless. Of course, always start with a backup. I highly recommend Titanium Backup for apps and SMS Backup+ for SMS and call logs, though given my use of Google Voice the latter is not as important. Titanium can upload to Dropbox which is a bit of insurance against the worst case. I temporarily disabled two-factor authentication on my accounts where I use Google Authenticator as a second factor, so as to not lock me out if I bricked my phone. :) All my Google data is synced into the cloud. Finally, I also highly recommend Xmarks for bookmark syncing between all devices. Because of that, my bookmarks are also all safe in the cloud. Just one last sync, and that was it.
Then came the fun part! I downloaded CM7.2-rc1 from the link on the CM wiki. I used ClockworkMod ROM manager to download the Google apps package. I booted into recovery to install. And then, uh, it got in a loop constantly rebooting. Pull out the battery to stop the loop and boot again. :) Just to be a little more sure of the state, I used the "install zip from sdcard" option to again install CM7.2-rc1 and the Google apps. Reboot and... Android 2.3!
That was simple enough I then downloaded the CM9 nightly and Google apps package again, and used "install zip from sdcard" in the recovery. I had no issues, and a few reboots later I have Android 4.0!
I'm having fun in ICS. It is chewing through the battery though.
YMMV, of course. Happy flashing!