What seems to have happened is that the new firmware is less tolerant of sub-standard RAM. Whatever the reason, many users are unhappy that some or all of their RAM is no longer functional, and want Apple to do something about it. According to Mr. Dasilva:
A web page has been set up to guide users adversely affected by Appleis recent Firmware updates to a petition requesting an immediate fix from Apple:
As you already know, many of us have lost a production machine to this update, with no fix or official response from Apple in regards to the situation one full week after the issue became known.
Please help us encourage Apple to do the right thing.
You can find more information about Appleis firmware updates at the Apple Web site.