Samsung doesn't give us an official way to downgrade but it is possible, although you'll have to reinstall all your applications.
I followed the instructions on this xda-developers thread but because I wasn't interested in rooting the phone, I substituted the rooted ROM they suggest in Step 3 and Step 13 with the stock Gingerbread-based firmware from Sammobile.com. The process is simple. First you flash the Carrier-IQ free kernel and then flash the stock ROM, and you are back to a fully-functional Gingerbread-based Captivate Glide.
Remember to do a factory reset after flashing, as you don't want traces of "GingerIceCreamBreadSandwich" messing up your setup.
And Samsung has now officially taken down their ICS upgrade page telling people to wait while they "fix" the problem.
Still wondering if we should all consider a class action against Samsung AND AT&T for allowing this to happen without proper testing prior to release. This has cost me time and money as a result let alone the fact that AT&T naturally continues to charge their outrageous rates for everything. Maybe it's time we sued for some money back. Anyone interested? Got some great class action lawyers here in Seattle!
BTW - I did manage to download a different Backup and Restore app (I used MyBackup free trial edition) and then went through the long process of resetting my phone and wiping everything. It did re-boot to ICS and not Gingerbread of course. I did remove my SD card where my backup was saved). Then had to restore all my apps and data after putting my SD card back into the phone and re-installing MyBackup (thankfully almost everything did restore reasonable well except for registrations and passwords - otherwise MyBackup worked like a champ!).
Literally had to re-install all my apps from the restore and so far my phone now seems to work 80% like it used to work. But still no backlit keyboard and poor Bluetooth functionality, among other things. And had to install a better power management app - burns up the battery like crazy.
Id love to tell you, but for SOME REASON it's stuck on 4%...it's been there for like an hour....WTF is going on? this is the second time it's just frozen on 4%...i d/ced it the first time and it was interrupted, so it's not like my computer is frozen...should I just be patient? how long does this thing take????
I haven't installed it yet or done anything, but I just got an OTA update pushed down. (I'm on the update that came out in September and did not install the recent update yet.) Anyone else got the update?
Edit: I installed the update. Keyboard back-light is fixed. Not sure what else has changed yet.